Re, mounting the rear camera, I agree mounting to the rear screen is not a good idea, due to vibration etc when closing the boot lid.
I have bolted my camera to the rear parcel shelf, as per attached photo and the power is taken from the power socket in the centre arm rest. I needed to use a spacer to raise the height to get an adequate view, within the wiped area of the screen.
I accept the limitation of driving without the parcel shelf in place for any reason, but I can live with that