Haven:
Only alternate units, except for Adepts, because I prefer Inquisitors here.
The exception is when the hero can apply all these buffs to the army himself.
Academy:
Only alternate units, excluding Mages (but only at the beginning of the game, when Archmages are much more useful, later on, Battle Mages are better) and Djinns (it all depends on the situation).
Inferno:
If I'm playing as Chaos, I only take regular upgrades, excluding Temptresses (unless the battle is against Necropolis). Otherwise, it's the exact opposite.
Dungeon:
Hunters, Minotaur Guards, Swift Riders. I decide about the rest as the game progresses.
Necropolis:
I decide about Skeletons as the game progresses.
Zombies are always Plague Zombies (it's easier to stand next to the enemy than to hit him + reduces defense; the exception is when playing against Necromancers).
Only Ghosts, because their ability is more useful, and their initiative is higher than Spirits (speed is lower, but I don't think speed alone compensates for that).
Vampire Princes, of course, for obvious reasons. If against undead, then Higher.
Until there are few Liches (less than 20), Higher; otherwise, Higher.
Until there are few Undead (less than 15), Death Knights; otherwise, Banshees (if against Necromancers, then only Death Knights).
I always have a dilemma with Dragons, but I usually choose Astral Dragons, but if I'm playing against Necromancers, then Spectral Dragons (because the Curse ability works, but Grief does not).
5. I don't understand about the Liches. With Resurrection, on the final stage, and with Weakness.