Conjuration (everything but dual cast and bound weapon perks)
Restoration (necromage/recovery/adept.. not a primary school more utility)
Destruction (frost/shock for damage because I will not use weapons aside from a dagger stealth kill here and there)
Enchanting
I need help deciding whether I should invest in illusion or alteration for my last school of magic. I won't be wearing traditional armor so alteration appeals to me (also for the paralyze spells and detect life/dead spells). However, I think illusion could be interesting because I could control my enemies (much like curses from the Diablo 2 necromancer if anyone played that). I'm leaning towards alteration only because I plan to use illusion on my assassin (illusion/sneak/archer/onehand/smithing), but I don't mind using illusion for the necromancer if it would 'fit' better. Thanks for your help and any suggestions!

. I'm going to go heavy into alteration OR illusion, but not both. I think I'm leaning more towards alteration, but I just wanted to field some opinions to see if anyone had experience.