You can actually print on vinyl to get multiple colors without stacking it. It's a foil type print so it's really durable. I ran a sign shop for 4 years and did all kinds of decals for bikes and cars and boat etc... You should follow cc700's advice about the graphics 'cause you have to go vector. The key is to find a shop with a vinyl printer and do as much of the design as possible. Ideally, you want to walk in with a disk with everything sized correctly and in vector. Also, don't forget to outline your fonts.