My personal suggestion for the first game after the in game tutorial:
I will share how i started and perhaps make newcomers an easier ride while first grabbing this game.
Pretender setup:
MA Ulm, Master Alchemist, imprisioned.
Give him
magic
F2 A4 W2 E3 S4 D2 N2 B2
Order 3 Prod 3 Misfortune 2 Drain 3
General
Your armies are slow to build as armor needs resources. Hence when you can build 1 or 2 other castles for more troops.
In every castle try to get many mages to research.
The best thing you get against AI is your provincial defense. even 20 points deter many AI attacks. vs large forces you need more.
In chokepoints you can pump it higher and that is probably enough to do it.
This pd thing is good vs the AI because its predictable. But a bad idea against humans. The good about this nation is that even a moderate PD works.
Tactics
Line shielded infantry in the front. Divide in 3, main group in the middle, Guard the sides against flanking moves.
Follow by unshielded infantry and back made of missiles and mages.
When you can build the heavier infantry as they cost the same gold and have more protection.
Research conj 3 and evoc level 4 so you can script for master smiths:
summon earth power, blade wind, blade wind, blade wind, blade wind.
If you reach only evoc 3 you can switch blade wind with iron darts (patch the game to access this one) can only casted by mage-priests of this nation.
Masters alchemist´s deeds
Once your pretender awakes probably you want to manual site search with him.
Check the manual for magic items. After the general list its a list with only the items that boost magic levels. That is the most important part of the manual i think its page 282. With this setup i believe you can build all of them and thus, access to any magic. Provided that your steel armies keep the enemies at bay you can experiment in your lab.
Summary:
Simple tactis in battle: Shields, pikes, missiles.
little micromanagement: less soldiers needed, PD.
Rainbow mage to experiment with items, spells.