The lack of funds, is a consideration on a new server or when started.

I fund new teams, with existing teams.
And actually had two accounts, each half full of maximum (70th at the time) level toons prior to getting into 5-boxing... so never really went through the not enough gold thing, at least by the time I started boxing.

I basically give each toon 1,000g when I start them.
So they can loot whatever, but don't actually need to loot at all (aside from quest drops), while leveling.
This, combined with quest rewards, allows them to buy mounts/training up to Slow Flyers.
Once they're done Outland, they have enough gold to pay for their own Cold Flying.
Once they're done Northrend, they have enough gold to pay back my AH toon, with interest.