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The only bugged Ice spell is blizzard. You might want to have a secondary element as a secondary for enemies that are immune to frost. Or a melee weapon or something.
And yes, kill Dukaan. He must pay for forsaking Alduin, praise be.
There are way better races to play a mage. Dunmer or High Elves are way more superior mages.
Btw, i think there is a rule against double posting.
Keep in mind a majority of the enemies you will face have at least some frost resistance(nords, draugr, frost dragons, frost trolls?), and destruction already doesn't do huge damage to begin with
In Skyrim, Dunmer don't make any better mages than khajiit.
It's not a buff, just naturally higher skill, so you'll end up with maximum of 100 just like mentioned Khajiit will have a maximum of 100. It's not like it's too hard to raise a skill up, especially with Mage stone.
That's true of most skills, just not destruction. It takes much longer to level than other damage skills(1h, 2h, archery)