I can help with those 2 questions Hitman as I a similar install on my 07.
If you don't want to remove the spoiler, start,by Removing the plastic skin like you mentioned, the hard part is get the heart to drill the hole, most cameras will come with proper size but really any normal drill will do, make the width the same width as the threads, the outer lip of the camera will anchor the camera in place. Insert the camera video cable and power line up thru the hole, pull the camera up snug, now from the top side, slide the angle piece washer and the lock nut down the cables, the hole is kinda tight but squeeze your fingers in there to start the nut on the threads, then use a flat Blade screwdriver or similar tool to spin the nut around till snug. Careful to align the angle spacer correctly soothe camera is facing correctly. Then it is a matter of running the cables along with the others down the groove and Tap the power into the reverse light wire and then run the video cable under the left frame and up thru the grommet by driver left foot area.
Removing the spoiler is not hard to do or reinstall. Just be prepared to buy (ebay)7 new clips after you break yours pulling it off and also some new tape. First tape up the top edge to avoid scratches and slowly start prying up, it's just 3m dbl side tape under there.
Once you get that off, slowly,pull from one side and each clip,will pop off as u go. There is also 1 nut in the hole area also holding it on, remove from the skin side.
Reinstall by reapplying the tape on the top edge and placing the clips,in the spoiler piece and popping back in. Easy peasy!