Don't buy gold, it's too risky and there's really no need. You make over 10k gold from leveling 1-85, not to mention collecting profs like mining or skinning which will net you even more. Pick up something like jewelcrafting later on and you can make a lot of gold easily (I make around 5-10k a day with JC @ 85).
Training is easy, 1-60 is all set out with quests in the same areas, making things a hundred times easier than it used to be. 58-68 is still a shit hole, outlands needs an overhaul. Once you get on to wrath, you start to make serious gold just from questing
Play whatever class you want to be. There are no right or wrong answers here.