Wow. Too many ?'s for one post! Your paint should never feel sticky. What do you mean by "sticky?" No wax will last for
years. It could have Teflon on it (the Lexus). "Sand buff" as you call it is not always necessary. Some proceed right to compounding the car w/o color sanding. Most body shops are able to do it this way. I'll try for a 3rd (or is it 4th?
) answer: you can respray a door w/o primer, just use a sealer over the old dewaxed and sanded paint.