I think i got up to 270ish and i started to get the lens to peel off. but then it got tougher and i started to pry, thats when it chipped. i thought i read somewhere someone said 350 for removing the lens. it really depends what sealant is on the headlight. start low work your way up.
As for the painting, sand lightly or scuff, clean, spray.
**edit: oh and because the edge of the lens is textured (gives a frosted like appearance) you don't really see the edge of the inside of the housing. So after you get the lens off, if you wanted to do a 2 tone type of deal you might want to check how much of the inside edge of the housing you actually see.