Like most people over here i get the main part of my gold from the 25 man heroic cataclysm raids.
Most bosses are soloable with one character so with 5 characters it really shouldn't be a problem.
I like to bring a couple of boomkins for mass destruction on large packs of mobs (BoT and Firelands), starfall kills thjose of really quick.
Running a 5 man team grants around 15K and a 10 man team around 27K.
Hunters are great just as well, have a tank round the mobs up put them in front of a few hunters and barage them down in a split second.

Optimal use of your garrison will grant you lots of gold a day as well, but it is dependable on your missions and luck i guess.