National Combat Spells
Meditation Sign (H1W1, automatically researched): this removes some of the fatigue from the caster. If this caster is a communion master then it will affect all of the communion slaves as well. Think of it as a weaker but free version of the blood spell Reinvigoration.
Earth-Touch Sign (H1E1, automatically researched): this targets a demon at long range with perfect precision and forces it to make an easy MR check or die. It's like a very easily resisted, demon-only version of soul slay. The range scales with holy power.
Welcome Sign (H1F1, automatically researched): this targets a unit at medium range with perfect precision and forces it to make an easy MR check or switch over to the caster's side. It's like a very easily resisted charm spell. The range scales with holy power.
Fear-not Sign (H1A1, automatically researched): this grants the effects of air shield and sermon of courage on all troops within a small area within close range. The size of the spell's effect scales with holy power. This is an excellent spell for Jomon since its troops have such a problem with arrows. While the spell's area of effect is very tiny, having an A1 monk (or better yet, a path-boosted Saigu) cast it a few times on some of your troops should markedly improve your force's performance in battle.
Teaching Sign (H1N1, automatically researched): this grants the caster a boost in ALL paths (magic and holy) as though they had cast Power of the Spheres. This effect does not scale with holy level and it DOES NOT stack with Power of the Spheres nor does it stack with a Crystal Shield. It is in all respects a no-research, low fatigue version of Power of the Spheres. If cast by a communion master it does effect all of the slaves. This allows an N1H1 monk to boost himself up to being an N2H2 during the first round of combat. Then he can bless, banish, or cast Sermon of Courage like an H2 priest would, as well as cast N2 spells. A Saigu casting it becomes an H3 who can then cast Divine Blessing as well as suddenly becoming a much more competent caster in the rest of her paths.
National Summons
Note that all kami are magic beings with an encumbrance of zero. Most of them are sacred as well. That makes them nicely thugable because they won't tire from wearing heavy armor, engaging in lengthy combat or flying all over the place. Also note that Tengu, while all sacred, are not encumbrance 0, nor are they magic beings. All Tengu are 100% lightning immune and can fly during a storm.
Contact Jigami (N1, 8 gems, Conj-0): summons an N2 which produces a total of 45 supplies. Useful for getting you a guaranteed N2 caster early on to start site casting Haruspex. It's also like paying a few gems extra for an endless bag of wine which can cast spells... and be killed in combat.
Summon Ujigami (E1S1, 6 gems, Conj-2): summons an H2, ethereal kami samurai. Makes for a nice thug, though he is reduced to an H1 when he leaves his home province. He can lead 120 normal troops and 80 magic beings.
Summon Karasu Tengu (N1A1, 4 gems, Conj-2): summons a sacred tengu commander. Tengu are flying samurai who can throw one lightning bolt per battle, are shock immune and can fly in a storm. They've got good stats and superior swords so they'll mess your enemy up BUT they have even less armor than a Wokou, making them very fragile. This guy is good for leading tengu soldiers around. He also has excellent precision so sticking a bow on him wouldn't be a terrible idea.
Summon Konoha Tengus (A1E1, 2 gems, Conj-3): summons 5 sacred tengu warriors. Like the Karasu Tengu but cheaper and they come in batches of five. They make excellent "attack archers" or "attack rear" skirmishers who can really ruin a battle if they manage to fly to the back row of the enemy's formation and start hacking up mages, commanders and archers with those wicked katanas of theirs. They're made all the more effective if you can hit them with a good bless or some buff spells first. Fragile but deadly.
Summon Kenzoku (S1E1, 8 gems, Conj-4): this is like the Ujigami (ethereal, sacred samurai kami) but better. It has awe-2, a magic sword and better stats than the Ujigami. What it can't do, however, is bless itself. Give this guy a good shield and winged boots and you have yourself a good raiding thug. With a bit more equipment and/or a decent bless (plus someone to bless him), you have a top notch combatant.
Contact Mori-no-kami (N3, 12 gems, Conj-4): summons an N3E1, sacred, ethereal kami with a short bow. Note that this spell can only be cast in a forest. While in the forest, this guy has good stats, stellar precision and he summons wolves at the start of battle. Outside the forest he changes to a tiny size-1 dude who loses his wolves and becomes an N2.
Contact Dai Tengu (A2E1, 35 gems, Conj-5): summons an A3E1N1H2 tengu mage-priest, 10 normal tengu with good armor and 15 normal tengu with crappy armor. In addition to being a powerful air mage, he can cast Teaching Sign and Fear-Not Sign to very good effect. You can treat him as a high end, flying Saigu. He's very good at following and blessing Ryujin, Tengu and Ujigami/Kenzoku with flying boots. His entourage is worth 10 or more air gems by themselves (and 5 mage-turns) so this summon isn't really as expensive as it might seem at first glance.
Contact Nushi (W2N1, 15 gems, Conj-5): summons a W3D1N2 crone who has awe-3, a serpent form and homesickness-20. Note that this spell can only be cast in a swamp. This is MA Jomon's only native access to death magic. Think of it as a Naiad for half the cost, who traded some nature magic for death.
Contact Kaijin (W3, 18 gems, Conj-5): summons a W3E1N2, ethereal, amphibious, water kami with a magic yari, magic net and a turtle shell shield. Despite the description, he does not lose magical power when he leaves the ocean. It's a good mage and can allow you to do watery stuff without having to pay upkeep for another expensive Ryujin.
Contact Tatsu (E3, 15 gems, Conj-5): this gets you a 1xFFF/AAA/WWW/EEE/NNN creature just like a Ryujin (if it were trapped in dragon form). It comes with triple paths and is the only native F3 mage you're going to get. Powerful but narrow focus and they suffer from having only one item slot (1 misc.). If you get an F3, E3 or A3 then it could be worth it, but an N3 or W3 might seem like something of a wasted opportunity. One curious thing is this is actually a double path (FF/AA/WW/EE/NN) commander with a magic bonus of +1. That means that if you empower it (say spending 50 blood slaves to empower it to be a B1) it will automatically become a 2 in whatever path you gave it. That's a 30 gem/slave savings right there. That's something to keep in mind.
Contact Yama-no-kami (E4, 22 gems, Conj-6): summons an A2E3N2, sacred, ethereal, mountain kami. He auto-spawns wolves and black hawks for free in friendly dominion (the higher the dominion the more he spawns), summons wolves at the start of battle, regenerates and has impressive stats. However, he loses one in all his paths if he leaves his home province. This is a very nice summon who can cast and forge all sorts of useful things, along with generating free flying/stealthy chaff.
Contact Kitsune (N2, 20 gems, Conj-6): this gives you a super stealthy fox spirit spy seductress with very variable magical paths. It has N3 + .5xAWES + .5xAWES + .5xAWES + .25xAWEN, meaning you could get an N4S3, an N3A1W1E1S1 or just an N3 on any given casting. It has a human female form and a fox form but there is no reason to go fox form except to go from map move-2 to map move-3. Paths notwithstanding, you cast this spell because it gives you a seducing spy. It has a stealth of 40, making it almost impossible to detect, and it has (in CBM 1.92 at least) one of the highest seduction ratings in the game. Give it a Cat Charm (seduction boost) and some basic combat gear (in case the seduction attempt fails) and send this literal vixen out to steal some enemy commanders. In a pinch they can also generate unrest, but that's kind of a waste of their talents.
Scales
You have a lot of options when it comes to choosing MA Jomon's scales. Before digging into specific builds, let's look at the characteristics of the nation which will influence our scale choices. None of your mages are old so you could take death without condemning them all to an early grave. However you have an excellent chassis for overtaxation, which benefits from growth. Your troops require a fair number of resources so production scales will help you expand faster but the case can be made that you don't NEED positive production scales... just don't take sloth or you'll have a hard time expanding quick enough. Expensive mages and nice castles want order for the money, but your troops are pretty reasonably priced and require a lot of resources so fully hiring from a castle should still leave you with money to spare for mages. Now, MA Jomon REALLY wants gems. It has so much it can forge, summon and cast that it is ravenous for gems. Taking luck and magic (and neutral Order or Turmoil) will get you extra gems throughout the game. Those Omnyo-ji you'll have cluttering up your labs will help take some of the sting out of misfortune so MA Jomon can endure bad luck better than most nations. You almost certainly don't want drain since the nation's research will suffer and cost-effective research is something MA Jomon can have trouble with. Conversely you really can't go wrong with taking magic-1. If you do decide to take non-neutral temperature scales, you should always take heat because cold will severely hamper your Ryujin.
The point is, you can go a lot of different ways with MA Jomon's scales. One build I like to play is a scale-heavy game with Production-3, Magic-1 or 3 and some combination of order/turmoil and luck. High prod for the speed expansion, magic for the research, and luck for the gems.
An alternate option is Order-3, Growth-3, Production-3 and then some amount of misfortune to mitigate the cost of 9 positive scales. This allows you to rake in unprecedented amounts of money courtesy of your high-admin forts and over-taxation (if you have a couple of Saigu in the province you don't even have to patrol... but if you need to patrol you have low-upkeep, high efficiency Jito and Onna Bushi to do it). More money = More forts = More mages and More armies. Plus you'll be able to hire those truly expensive mages of yours with abandon.
Another build you can use is to reduce Production to 1, and going for Magic 3 with Misfortune. High Magic means that when you get lucky, you are more likely to get Gems of one sort or another. Production is great, but the Bushi require far less resources than the Samurai of later eras, and the Sacreds are also pretty cheap on resources, so you can get most of what you need with only production 1. With Magic 3, you'll find that research with your monks is fast, allowing you to access many of the better summons earlier in the game, like the Dai Tengu. Growth 3 is nice to offset the loss from patrols, but with the Jigami (an readily accessible, conjuration-0 summon) supplies are not needed, and aging isn't an issue. Order 3 is a must to take advantage of the powerful and expansive Ryujin. Your best recruit anywhere mage (the Onmyo-ji) isn't sacred, so you need the money to afford the upkeep for these units. With Cold Blooded Ryujin, Heat might be a nice perk for you. The lose of income is terrible, but doesn't effect your underwater provinces, and if you can push your domain, it makes conquering provinces a little easier.
Pretender
Your national mages can cover most of your magical bases just fine once you get the desired path combinations. This is especially true of air, earth, nature and water. You are kinda weak in astral and fire, and have no death magic to speak of. Blood is right out. Your military should be able to expand fairly well without assistance (unless you took sloth scales) so you likely won't need an awake SC. You have nice recruitable sacreds and really weak priests, meaning you'll want a good Dom score, if only to prevent your provinces from being overrun with black candles. Finally, you need to ask yourself if you want to set up a nice bless for your recruitable and summonable sacreds. Just realize that any bless you choose for your sacred melee units is highly unlikely to map well onto your sacred Miko archers.
An
awake Lady of Fortune with W4S4 and Dom 8 will help spread you dominion, make getting into the water a little easier, get you some nice lucky events, and offer a modest but helpful bless to your sacreds. She'll be able to forge high end astral items for you as well as toss her weight around on the battlefield once you give her some equipment. This gives you room for a net of three positive scales.
Similarly, an
awake Lord of Plenty with E4S4 and Dom 6 can go site searching on the heels of your first conquest, all the while generating delicious earth and astral gems. This leaves points enough for a net four positive scales.
A
dormant Celestial General with E9A4 and Dom 7 will give your sacreds (both combat and mages) a nice bless, generate extra troops once he wakes up, be able to forge air boosters plus elemental staffs, and be capable of cloud trapezing into a battlefield and casting earth magic with abandon. This leaves you with a net of one positive scale.
An interesting option is to take a
dormant A2W9 Lord of Storms with Dom 5. You'll have to be aggressive building temples to keep your dominion strong (have your Omnyo-ji forge Stone Idols to help your priests remove enemy dominion) but you get points enough for a net four positive scales and you give your sacreds a very powerful bless. This is especially true for your Onna Bushi and Tengu who already have a high defense and rely on it to keep them alive in melee. And later on your pretender can cloud trapeze in to drop jaw-dropping water evocations; even something simple like Falling Frost covers a HUGE area when cast by a W9 mage.
An
awake F1D4N4S4 Crone with Dom 5 gives you a nice site searching rainbow mage who offers some useful blesses to your sacreds. That 1 point of fire allows her to forge flaming skulls to boost your otherwise tepid fire mages up, and the death bless will make all of your sacreds, including the Miko and your sacred mages, inflict extra afflictions when they damage an enemy. This leaves you with a net of three positive scales.
An
awake F3A2W2E2S3D2 Great Sage with Dom 6 is the quintessential research pretender. Leave him in the lab and he'll get you an extra 31rp each turn, which will let you hit those research milestones blazingly fast. He even leaves enough points left over for net two positive scales. Once you have enough lab jockeys to cover the research, send him out site searching.
An
imprisoned S9 oracle with Dom 6 will give your sacreds a nice bit of survivability, give you major astral oomph late in the game and, most importantly, afford you a net of nine(!!) positive scales. In this case I'd take Order-3, Prod-3, Growth-3, Magic-1 and Misfortune-1 and then tax the peasantry for all they're worth. An admin-50 fort + 36% scale income boost + 130% taxation + 2 Saigu calming the population = a WHOLE lot of money from your capital which you can maintain indefinitely with almost no population loss.
Research Goals
As MA Jomon you have a whole lot of different kinds of magic you can toss around so your research should center around two things: finding what gems you'll have access to, and climbing up to at least the middle stages of conjuration. Researching Thaumaturgy 1 and 2 gives your Omnyo-ji something to do on the battlefield in case you face an early rush (communions, bonds of fire, mind burn, desiccation), as well as giving you access to the air, earth, fire and nature site searching spells. If you are facing an early war, you might want to switch to Evocation 1 and 2 next... and maybe pushing for 3 while you're at it. That gives you more effective combat spells for your communions and lets you start ritual-searching for astral sites. Regardless of the particular order, you'll want to reach Conjuration-3 and Evocation 2 or 3 as your second and third research goals. Conjuration-3 gives you ritual water site searching, access to a slew of handy national-only summons as well as most of your combat path boosting spells (Earthpower, Phoenix Power, Water Power, Power of the Spheres) to boost your combat casting potential up to mighty levels.
From here you'll have to decide what you need based on the nuances of your game. If things are peaceful enough, you can push for Conjuration-4 to get access to the excellent spell Voice of Tiamat (which will turn those water provinces you've been conquering into gem gushers), the very nice path booster Strength of Gaia (gives your mage barkskin, regeneration, +4 strength and +1 nature magic), as well as access to your chief thug chassis, the Kenzoku. Alternatively, you could start climbing up Enchantment or Alternation for some nice troop boosters (strength of giants, fire arrows, haste, antimagic, body ethereal, luck, wind guide, etc.). And Construction justifies itself. Once you realize which types of gems you will have a lot of, and which types you'll be short in, you'll want to direct your research to capitalize on that info.