I usually go in at 36 with a mage. Followers' spells are still dependent on the level you first encounter them I think. Either way it's still rewarding to tell J'zargo that you already know the Expert Destruction spells. He's all like "wait, what?".

When I want to raise my skills without actually using them in combat(like spamming telekinesis or rally), I just pretend that Im 'practicing' my magic at the college. Kind of like how you see the other college members practicing their spells in their rooms.

Most things will be levelled so it's not that big of a deal. I did it at level 45ish and I was able to destroy everything except for the

(this could be considered as a spoiler, it really isn't but I'll just be safe and hide it)

The only real threat is going to be Morokei.

The Caller can also be quite a threat if you're unprepared.

As always, I shall recommend conjuration as a most for all mages. Only superstitious cowards fear it, and they should. Having a portable tank (Frost Atronach/Dremora Lord) for melee enemies is essential. For Morokei specifically, Storm Atronachs are great at svcking up all his lighting magic.

Oh yes. The Storm Atronach I summoned from a staff completely locked Morokei in one position. My follower was firing arrow after arrow, Storm Atronach doing its thing, and my character throwing Firebolts. He didn't give me that much trouble.