Should it go specialized caster or not? If it specializes on necromancy, which schools does it exclude?
According to this book:
[ame=http://www.amazon.com/Strategy-Dungeons-Dragons-Fantasy-Roleplaying/dp/0976808501]Amazon.com: The Power Gamer's 3.5 Wizard Strategy Guide (Dungeons & Dragons d20 3.5 Fantasy Roleplaying): Goodman Games Staff: Books[/ame]
Specialization is almost always worth it from a mechanical standpoint.
It was written with just the Core3 in mind, but I think the analysis generally holds up. And, IMHO, if you're going to specialize, you might as well go Focused Specialist (PHB2). For a BBEG- here, a lich- anything you give up will have a price, of course, but its balanced out by the fact that such a foe will probably be well prepared and in its lair.
In this case, I'd say that you could probably do without Transmutation. Its my favorite school, but I think it reaches its peak utility when used in a party of equals or near equals. If you want to do direct damage, you need to keep Evocation or Conjuration, but you don't need both. Illusion and Enchantment are both similar in that they "judo" your foes- again, you could probably do without one or the other. Personally, I'd keep Illusion, for reasons partially delineated in this thread:
http://www.enworld.org/forum/d-d-3r...g-dragon-vs-high-level-party.html#post4826842
While Necro seems an obvious one to keep, its not essential. Some of what the school grants overlaps with the inherent abilities of the Lich. There's nothing wrong with improving one's strengths, but dropping Necro in favor of keeping both Evocation and Conjuration for instance would mess with the players'- and PC's- minds, as the BBEG keeps tossing off damage spells and summons while the necro spell they're geared to fend off never comes...
I'd also look into Reserve Feats that match its spell selection, the UA spellcaster variants (esp. those that sub for Familiars), and maybe even something quasi-exotic,
like racial substitution levels (if any apply). (Missed that thing about him being human...)
For example, while they're considered "sub-optimal," the Heritage feats from CompArc give a nice wrinkle to any arcanist. Sure, you'd need at least one level of Sorc to qualify, but once gained, it works with all (level 1+) arcane spells a PC knows...and as a spell-like ability can be used while grappled, etc. For a specialist who eschews the Evocation school, they can provide a touch of direct damage dealing- with an area effect. If you pick Infernal Sorcerer Howl, for example, your BW would be a sonic weapon...something that few parties will be prepared to resist meaningfully. The output isn't high, but you probably won't need it to be.