[Amorphous]

Reading guides here on the boards is a very good way to learn, but you need to keep in mind that in some ways SP and MP differ a lot. In SP there are a lot of things you do not need to worry about from the AI (like effective SCs and good mage usage), but on the other hand some MP techniques do not work that well (like light raiding thugs).

As you have noticed the AI recruits a lot of troops, so you need to be able to scale up whatever you do. Now, TC has a lot of good mages and that is what you should concentrate on. Your troops are there to defend them and mop up the pieces of the enemy once the mages are done. Buy and buff your troops accordingly. Buffs like Wooden Warriors and Legions of Steel make even the low cost, low resource troops adequate defenders and that with relatively low encumbrance. That last is important, because in drawn out battles fatigue is a killer. Also it saves you a lot of money.

Same really goes for your glaive troops, but here it is about offence. They are not there to defend, so go with the cheap ones and buff them with Strength of Giants (and Weapons of Sharpness when you have it) for some extra punch.

Then you can start helping your troops by de-buffing their opponents. Consider Curse of Stones here, tired troops are easier to hit and have trouble hitting you.

As Jarkko said, slowing the Machakan spiders down is important as it gives your mages, bow- and crossbowmen time to finish them off. Jarkko gave a number of good suggestion and you should look through the spell list to find out what suits you and your mages. You do not always need powerful mages to get the job done - Swarm is e.g. a great spell for slowing down armies and the caster only needs to have N1.

This brings me to my next point which is the importance of not just using your top mages. You can only hire one Imperial Alchemist or Celestial Master per turn, which is far from enough when fighting multi-front wars against the AI. There are plenty of ways to use your non-capital mages, even if they do not have (enough) magic paths especially suitable to the situation at hand.

To take an example the Master of Ways always has a water pick, which means he can cast quicken self. If his other pick is not of any use in the current fight, hand out an Ice Pebble Staff. A couple of quickened Master of Ways with Ice Pebble Staffs can freeze a number of enemy squares very quickly.

Communions are great, but if you have trouble bringing it together there are plenty of things you can do with S1 casters without it. Have a higher level astral mage cast Light of the Northern Star. Your S1 casters are now S2, which gives them a lot of options. Against the AI hordes you could consider Stellar Cascades. It is a S2 spell with decent range, good area coverage and relatively cheap fatigue-wise. It does AP stun damage, so a number of mages spamming this will quickly make large swaths of the enemy troops very easy to hit and crit, if not pass out completely.

When you use decent numbers of cheap mages, a lot of spells that seem to weak on their own start to look very enticing.