At that level it might be good to go for destruction. You will be questing your way through the BC levels anyway because grinding isn't as profitable here. You can get a level per evening doing quests. And you'll be upgrading all your gear a few times as you level through too so now's your chance.

In my limited experience, and from what I've heard/read, shadow is far superior to fire though so you may want to go for a mixed build or choose your talents accordingly.

Anyway you can always respec to affliction if it doesn't work out!