/\ the exhaust will work with a motor swap, but it will be very restrictive. You might want to look into a used aftermarket 2.5" exhaust. #5, Yes, a coupe spoiler will fit a sedan, this is a well known swap. For #9, just spend the money on the endlinks, you'll be happier. #10, yes, the RS has sideskirts, black plastic from the factory.
Also, are you going to keep the 4eat or swap in a 5mt/6mt?