Kristian did the headlights and i bought them from him.. Pretty sure when Naps did his he used normal paint too.
I can't see heat being a problem to be honest, it's only the outer lip of the light and maybe the indicator housing you'll be painting, won't get that hot.
I'd use gloss, but i don't think it matters too much really..
When your sticking the lights back together though, make sure you clean the inside of the glass and stuff.
I got polysterine in mine from the packaging i can't be bothered getting out, it's annoying though!