I did look into an S3 bumper on mine, it is the same mounting points as an a3, I have seen S3 bumpers on A3s parked up and driving around, the S3 sides of the bumper sticks out a bit, but not much more than standard, you should get away with it, one of the members did and S3 front and back bumper on his 5 door if you wanted to look though all the pages of photos, looked really good. I think front S3 wings will also fit a 5 door, but I think it would look odd with wide arches on the front and standard arches on the back. Five door was a good choice, may not look as good as a 3 door, but they are massively practical. You would need the S3 grill to go onto the the S3 bumper as they are different sizes and you can also but an s3 spoiler on the tailgate too. Does it have the facelift projector lights in? The look really nice with an HID kit in. Mine also looked better with the S3 exhaust system on the back too. At the end of the day it is down to how much money you want to put into the car, in the end I looked at what it would cost to do all the mods like leather, RNS-E nav unit and then getting it set up on a rolling road and ended up getting £3K back on my A3 and adding £2k to upgrade to a 2005 B7 A4 with bi-xenon lights, leather and RNS-E unit.