If you're looking for coverage of large areas, there's nothing wrong with using spray cans. If you go with a good "name" brand paint, it should work just fine.
I've used spray cans on many projects with no problems. I have an airbrush as well, and it comes in handy if I need to paint something a specific color that's not available in a can. (Of course, most of the accurate Boba colors aren't availabe in sprays :facepalm )
For painting on metal, look for self-etching primer. It's usually made for painting on metal, and should give a nice tough base coat.
Make sure you let it dry really well before putting on your color coats! 