Sometimes itches. Most of my kids have no mention of pain with this illness but occasionally state that the lacy rash they get over their arms/legs/trunk is a bit itchy.
No. It may itch a bit, but it doesn't hurt. So if the rash is painful, it is something else, in all probability. And for the record (this is one of my major pet peeves), a rash can only occur on the skin, so "skin rash" is redundant; there's no such thing as a "hair rash", "liver rash", "kidney rash", etc., etc.
Heat. It is called slapped cheeks so there may be heat. Pain is not normally noted. Resolve within a few days without any treatment.