I've gone through chapter 1 blind so far, but then read some of this topic and learned about the ton of endings this game has. Is there some optimal way to get all or most endings while repeating the story as little as possible?
Also, are there any strategies, units or other tricks that you can recommend using?
you'll need several playthroughs to get all endings. what we have on the top of my head are law route with good endings (i think you can get corrupted there too but no real reason to bother since you will go for corrupted n chaos anyways) for each heroine. then there is conquest route with Corruption endings, True Odin ending. Harem ending and Fina+Menia ending/ there is also 3 sisters ending which you can get in any route.
Al of the above demands strict affection/corruption control. you'll need to calculate every answer and affection gain from it. if anything i would recommend playing just for fun first time around. and go find a walkthrough for a 2nd run.
As for unit combos - really depends on difficulty. normal steamroll-able by generally anything. anything harder is suffering.
overall good places to start with units.
1)Make a night squad. (look for crescent moon on a dark background icon on the unit properties, mostly undead and demons+some beasts) those will be really strong in night battles. (time of the day strongly affects unit strength)
2)Make a treasure/Bounty hunter squad. fill it with units that have th or bh skills (also argument them with medallions) that unit will be your source of income and weapons.
3) easiest game plan is making use of "boost" skills. stack them. like boost beast will boost every beast (paw symbol in status panel). you can either go with "feel squad with beasts that boost all beasts" or maybe build support squad around 1 or 2 strong units that can AoE whole enemy team.
all in all learn what skills do. learn what each symbol means. it would be enough - especially if on normal
edit: oh also save the keys till you get 10 - if you use 10 at once you can get units that you wont get normally until several runs into the game.