Where do the crews get the money they need to buy and repair gear and food?
Do they have jobs or do they get allowances?

Well they get money and gear from winning in races.

Artha once said in The Stand That "With this new level 6 gear, (Word's disguised wraith gear) we can enter a higher level race, we'll get a lot more gear and Drakels, plus better standings!" They get what they need by winning races. It appears that Dragon City's other inhabiants have jobs though, as Dragon City appears highly industrialized, and someone has to keep all that equipment running.