Lore of Death is amazing against most armies for attacking (I know your on the defensive but just in case...) and for defence Lore of Life. If you wanted a mixture Lore of High Magic is great. As for magic items, (for your Archmage) I would have the Sword of Battle or Sword of Strife as he is really weak if he gets into close combat and the Channeling Staff as it helps him get extra dice to roll. For your Mage I would choose Earthing Rod and the Seed of Rebirth. For your
BSB, Ruby Ring of Ruin or Khaine's Ring of Fury as well as Armour of Silvered Steel and Dragonbane Gem. All these
IMHO are amazing and I always use them with my High Elf army. Hope this helps