Definitely agree with the advice on making sure you have farming skills on your first char. Old world mining / herbs go for great prices on most servers.

But regarding the AH, I wouldn't necessarily tell people to stay away. Making money, even at low levels, is so painfully easy these days. When you can unload that stack of copper at 5g per and then later that stack of tin for 20g, it adds up quickly. And quest rewards in the old world are very hit or miss. There's some great things at times and then you get a stretch where there's nothing but +spirit gear offered.

So if you're making a decent income and the new shinies at the AH are appealing, just buy them without guilt. Feeling overpowered for a few levels with your new purchased blues can make the game easier and quite a bit more fun. You can look at Wowhead to get a rough idea of how much something sells for and to make sure you're not getting ripped off on the buyout. As long as you don't go too crazy, you'll easily have enough gold to buy your epic flyer and to purchase stuff that's excellent for leveling.