Just keep the machined surfaces paint free. Tbh I painted mine completely (a thin coat) and all has been fine but better not to risk it. Anyway, that should all be hidden by your chrome hubcaps!
If you race or end up driving through many mountains you might bubble off a bit around the outsides but otherwise not. I've had brake fade a couple times and there is some bubbling.
The paint will either bond the wheel to the drum or it wll fall off because you have a depleting layer between the mating faces. Use coppaslip on the mating face of the wheel/drum. Of course you can paint where the wheel does not touch the drum.
Nope, it's been fine for 30,000 miles. Wheels on and off probably about 10x. Paint still intact and OK. As I said, it's a thin layer though and they were all sandblasted beforehand which has probably helped. To be safe, it's definitely better to go paint free. I couldn't tell you how to stop it coming off for sure.