With my wife deciding to play a Mage, I also added another character and account to the mix. I decided to go with a Dranei Paladin, to act as a tank for all the other characters. With my wife, we will be a four person team. I think that should be fine for handling most of the Pre-BC content.
Hunter and Priest are 19, Paladin is 14. About 50 Gold to go around.