i can't answer 1-3 sorry. I bought such a disc for my Roadster as plain ali so I could polish it. I would imagine your dealer ordered it sprayed.
It will scratch the paint where it touches the rear skin of the car. I tried a neoprene seal but after 1k miles it had started to wear. Spacers might help.
I would imaging it comes with the ctentre hole . Mine did.
