I started out in FR with a necromancer from Thay, I chose the shadow weave feat (really cool in its own right) and took evocation as my barred school (more of a personality choice than anything else, but man do I miss tossing fireballs).
He's 6th level now and chose the Shadow Adept prestige class. It seems to work pretty well. I'm also trying to keep my illusion and enchantment schools up to par with necromancy so I have more variety of spells to cast. Fair warning though, you can pretty much forget the flashy spells, pardon the pun.
Divination is actually a really handy school, especially if you don't have a cleric with the group. I would also recommend taking Healing Touch from Magic in Faerun at first opportunity or toss some ranks into healing. You should also be prepared to serve a support role, especially if you take the same route my character did. On the plus side, your buddies tend to owe you their lives many times over, a real plus if you're CE and need allies.
If you're dead set on mastering undead, I would say go for the True Necromancer PC for the long haul. If you want to stay pure mage you won't be animating dead for many levels.