Spraying with rattlecans-amount needed?

If you do not want to strip the whole lot of the old paint AND providing the the underlying frame is in good condition(no rust), you could get away with roughing up the surface with sandpaper to give the paint something to grab. Then you could dispense with the primer.

5-6 cans for a good job + primer.

No there's no rust, maybe a couple of spots but I can get rid of that with some steel wool or fine sandpaper, so nothing serious.

5-6 cans is noted! So I need clear spray as well for the shine, or will just the paint do it? I reckon it'll protect the paint from scratching very easily as well..