What Khatovar says. RAF questing, which is how I've levelled all my guys, is so fast, and gives so many quest rewards, that you'll spend more time vendoring gear than buying gear. I've had one or two guys end up in Outland with one item of starter gear (boots or bracers usually) but they get replaced as soon as you do the first few quests in Hellfire Peninsula.

Dual boxing is going to be a bit slower than five boxing as you won't kill things quite so fast but at least you can do some of the collect quests quickly.