However, Im playing a dual wielding warrior. Im thinking of making a Vamp Lord centered mage build on legendary difficulty. I tried it for a minute (saved then accepted Harkon's gift, fooled around with vampire lord form for a minute then loaded and rejected it) Which beast ring to use? When to turn back to a normal Destruction/Alteration or Conjuration/Restoration vampiremage? Should I do pure mana/mana regen for enchants? No alchemy no smithing, though I might try RPing with Vampire (after the DG questline Royal) Armor, though giving up Alteration on a mage stings

Plus for close combat you get melee Vampire lord and paralysis

It will be very tough on legendary. When you transform to VL form, you lose all armor. You gain health, but with no restore spells or potions available, you'll soon realize that high level enemies will be able to hit you for a lot of your health. A couple of hits and you're dead.

I'm not trying to discourage you, I play a vampire and go into VL form on legendary with mods that make enemies more powerful. You'll just have to pick your spots and be more careful than normally. It's quite a good challenge actually. VL is actually much weaker than being normal at high levels, not more powerful. Just keep that in mind and you'll do great.