You don't have to get all of the original paint off. I didn't on my build. However I did sand the entire frame to roughen the paint, get the surface layer of paint off, and get rid of any wax, grease, etc on the frame. Then started laying down the primer.

I used DupliColor paints which can be found in just about any WalMart's automotive section. I used their "Metal Specks" or what ever it was called line which has a LOT of metal flake in it. I was happy with the results, but as other more knowledgeable painters stated later, the paint type (polyurithane I think?) isn't super durable of a finish. Also, I learned the hard way, that the DupliColor Metal Flakes will come RIGHT OFF with products like Goo-Gone, etc.