Reason not to buy off the AH is because you can get gear that suits your needs from quests and dungeons, thus saving up eventually for epic flying and cold-weather flying. Not sure what you mean about mages having trouble in WOTLK, though. If you look at the thread about AOE leveling, you'll see complaints that we can't find enough areas that have 12+ mobs to round up and kill all at once. And that's solo. :) I'm just lvl 76, but besides needing help with a few of the Wanted quests, I've solo'd pretty much all the way.
I disagree bout skipping dungeons, though. It's not the fastest way to level, but it's a very good way to learn your class in group situations, which are fun. :)
But a lot of good advice was given in this thread. Fact is, you wear cloth, and that's all you'll ever be able to wear, so you have to play with that in mind, and be prepared to blast something down before it gets to you (or run).
As far as professions go, if you can get a friend to loan you 100g and you follow the enchantrix/bottomscanner guide in the tradeskill forums, you'll be able to pay your friend back in a few days and start making some bucks on the AH selling mats. At least it still works very well on my realm. That way you end up with enchants for your own stuff, as well as for friends, + ring enchants, etc. Personally, I had a hard time with herb/alch on my lock, because I'd run out of things to skill up from in the areas I was in, but I could have been doing it all wrong. But herbs are selling very well right now, so herbing is def. a good way to go.