Hopefully someone will post a decent guide as I am no expert at mp or Jomon. But I've got Jomon in an upcoming mp game and I'd like all the advice I can get. And I have been playing them a little because of it. The Shinuyama guide is good on the summons for jomon as they are the same. I think Zenzei's Flame arrows is a great aim to go for. Your Longbow Samauris are a key unit.
I am sure the W9 Dragon is good but I am not sure that Jomon is an especially bless strategy friendly nation and it wouldn't be my paths on a Jomon pretender. You do have some sacred summons (iirc), but the sacred troops are capital only and don't really excel at anything and are as resource intensive as the rest of Jomon.
Your national mages are decent all rounders but they can't summon most of the national summons. Therefore I think you really need them on your Pretender. You need some death and some fire to get your best summons (Dai Oni). Air, water and earth add extra summon options too. Quite frankly the manual suggested awake Ghost King with D3, F2, A2 & E2 is not that bad for Jomon.
The ghost king is not the best awake SC points can buy but you can get the extra paths fairly cheaply so he will help with early conquests (with the army) then provide your early summoning and finally some decent forging options. I usually operate him with my army as he is a bit frail for an SC and losing him is a disaster. His etherial nature helps when your samauri are peppering the enemies he is fighting too. But try and script him and them to hit different things.
While Jomon is very resource hungry and therefore cries out for Production scales it has been pointed that you are usually better off going for extra cash (order or high luck) and then building another castle soon. That is the usual 'rule' for multiplayer Dominions anyway. And goes for most - some would say all - nations. Your almost always better off with Sloth 3 and 120 points in the 'bank'.
But in Jomon's case your small and poor quality starting army plus crippling resource intensive troops makes either an awake SC or high Production scales needed if you are not to get off with a very, very slow start. Which will kill you in mp. The Jomon's starting army struggles against indie 5s IME and won't take one a turn unless you are very lucky. You simply can't build anything decent at under about 24 resources a piece (and even then they are not exactly good) so you won't be able to even replace early losses let alone boost the army until you have the capitals surroundings conquered.
Also as you pick up new areas you may want to build some troops with shields to protect your Samauri from these provinces. It is suprising just how many indie chaff you can build with just Production 1 after playing so often with the traditional Sloth 2/3. You can then build purely samauris at your forts. So I think Jomon is one of the very few nations where a positive Production scale is a possibility. At least consider it.
Money is seldom a worry for Jomon. Your top mages are only 160 each and your troops are cheap (and too resource expensive to mass). So you could consider taking less order and can get away with it. I think Turmoil/Luck is good for Jomon as the bonus gems and cash it generates are very useful. Plus the Heroes of course. Picking even +1 positive production seems to greatly increase the appearence of the resource boosting mine finds too and these are obvious sites for new forts.
I like a bit of magic too if I can aford it with Jomon. You will recruit a lot of mages (as they are not capital only) and it's a decent research boost. And it makes the cheaper 90 cost mages actually more efficent as researchers.
Quite frankly Jomon's strength is not in it's troops - although the Samauri LB is nice - but you just need to get in to the middle game when your summons & mages can take over. Without a plan for the early turns you will be easy prey in mp. So an awake SC and/or Production scales are needed to keep you in the game.
You have another problem though. Most of your good summons require death gems. Ghost generals (nice Thug) and Oni Generals (ditto - but why not get a Bane Lord instead?) and finally the Dai Oni - practically an SC - all require plenty of death gems. Plus the better Oni troop summons want Death (or valuable Fire) gems. Although I am not really sure that the troops are as useful as the Thugs.
But Jomon has no death income and no death mages. So your pretender needs enough to at least summon a Revenant or two to start remote site searching as soon as possible. Happilly Revenents are Enchant 3 so you pick up the ability on the way to Flaming arrows anyway. Some alchemising is going to be needed for that though. Plus a bit of searching by your mini Rainbow Ghost King. You see he has no end of uses
It's another reason high luck is useful. Getting a couple of death gem finds can boost you a lot early.