I wouldn't be too demanding of poison staff - others will work better until you find a good poison one then others will come up better until the next. The way I did it (albeit, not with an undead) was just in general. Robes when available, high magic defense, etc. I guess for an undead, you'll just have to go with a cowl head armor.
My main question wasn't equipment; it was which stats to build on since few are available (one devastating level 10+ like geomancy or two types not quite as strong, etc). I think I made my battle mage both too weak in melee and magic usage. How much memory compared to intelligence, warfare, and say, single-handed? For my battle mage, so many areas were needed that none got very high. Still, he's tougher then the average mage (for taking hits).
