Update: Wearing four pieces of the armor of Ahzidal adds 10 to your enchanting skill (12.5 for necromage vampires). This allows even better gear to be crafted along with necromage vampire and the black book. Now 2702you can craft fortify smithing/alchmy enchantments of +43%, smithing potions of +243%, and enchanting potions of +61% (all numbers are not including the additional 25% necromage bonus). The most exciting thing is now you can enchant items which reduce magic school cost by 43% when worn by a vampire necromage the additional 25% bonus makes the reduction 53%. So you can have zero magica cost in a school with just 2 enchantments. This means if you use a circlet and pen oc helmet ( which matches perfectly with the black vampire armor) you can have 100% reduction in all five magic schools.
Update: did some experimenting with weapons to see what the most damage I could get. I crafted five fortify archery items of +87% this pushed the damage of my ebony bow to 2702 base damage. I dual enchanted chaos and shock the chaos did 283 damage and shock did 182. Shock can be switched for 118 absorb health instead. Fortify marksman potion was 243% and death bell + river Betty poison was slow 50% for 304 seconds and cause 304 damage. Bow damage after drinking potion was 10,909. That would give sneak attacks over 30,000. All of this without fortify restoration. Of course using these would make the game boring as hell. I would recommend only using the necromage crafting abilities for things like spell cost reduction instead of increasing damage. Once weapon damage gets over 100 -200 the game becomes too easy.