Any Race can really be a Battlemage, or a ThiefSage, or even WitchWart.

At some point you will pretty much have mastered quite a lot, race makes no difference.

Dark elf is the appropriate choice.

Doesn't matter anymore because of the loss of attributes, birthsign, and racial skill bonuses

If you wanted to go by "old school"

Generally races with high Intelligence/Wisdom/Skill bonuses made the best mages

Breton and Altmer could generally be any type of mage archetype
Dark Elves make good mobile + destruction types
Argonian Females made good potion brewers and mystics (soul trap, detect, reflect, absorb, dispel and telekinesis [wherever those affects have gone with the loss of mysticim])
Bosmer: Semi-decent potion brewers (if you want to count that as magic)
Imperials: Make good Agents, Knights and Bards (basically Illusionist + Personality based Assassin, Warrior, or Thief type) Hard to classify those for you without being specific on Elder Scroll class examples
Nord Females: Fighter / Restoration
Orc: Any armored caster using destruction, restoration, alteration

Races that are non-traditional at being good with magic (low attributes, and low or no skill bonuses for magic)
Argonian Males
Bosmer
Imperials (except Illusion)
Khajiit
Nord Males
Redguards

I don't really play as this race but i'd say Dark Elf. I think they are a well-rounded race. Plus they have some good race attributes to boost

Any of them

Any. The skill bonuses don't matter. They can be made up in a couple of levels. Pick which one looks best to you. The only other deciding factor could be the traits, but they really don't matter that much. It just depends on with you think you may benefit more from. But in reality they will be a mix, so it still doesn't matter.

I have a Nord BattleMage, but im considering changing to a class that has better mage attributes.

Any thoughts?