Well, why didn't you just say Gandalf from the beginning?

I've tried this myself, but didn't get very high in level (I was doing sort of dead-is-dead, died, kept playing anyway, and then just got interested in other character concepts).
But, for what it's worth, here's how I would see this kind of character. You've probably thought of all this already, but I feel like typing:
Race - Imperial. Voice of the Emperor simulates Gandalf's authority over kings and enemies.
Restoration - OK, there's no description of Gandalf healing anyone, but this really seems to fit with the whole 'white magic'. I can also really see Gandalf casting Wards.
Destruction - I wouldn't necessarily take it to 100. Gandalf wasn't about 'flashy' magic. Cloak spells are thematic, but probably too weak for the cost. Runes seem to fit, too. Some occasional firebolts. If you have a sword (or staff) in the other hand, there's no need for dualcasting or Impact.
One-handed - self-explanatory.
Alteration - Protection is good, since you'll likely be wearing robes.
Enchanting - I'm torn about this, actually. Mostly I'm uncomfortable with the ethical implications of soul gems. There might be some conflict here with Gandalf's morality. And even without that conflict, does it fit thematically? You'll probably need to use (found) soul gems to recharge your staves/sword, though.
Speech - it would be great if this were easier to work up, because it would really simulate (like Voice of the Emperor) Gandalf's diplomatic side.
Illusion - I hadn't thought of this before, but I guess fear spells would be fitting. Maybe calm too. Frenzy doesn't fit the concept, really.
Apart from the above, you'll be using staves for damage as needed - like when you're maintaining a ward in the other hand.