I've no first hand experience with Plasti dip however I have seen other bikes that have used it. They all had peeling issues after less than a year. Not sure if this was due to the product itself or how it was applied. If you don't like it though or it starts to peel you can remove it without damaging the underlying paint with a nylon mesh dish scrub pad and acetone. NOTE: Do not use the green 3M scrub pads as they contain abrasive particles that will damage your paint.
a) that's completely normal, especially if friction is involved.
b) your fingers all you need. Especially if you are not a cheap bastard and you did put the 4 coats as you are supposed to.