R32 valance will fit the directly onto GTI top half of rear bumper, the exhaust will be costly part, I would recommend a decent brand for the back box as with time if you go cheap you'll end up hating the noise produced after a while.
Another option would be to delete the back box completely and just put straight pipes with tips but then again you have the issue of the noise. I can say deleting the back box will make no difference to performance, some people will claim turbo back pressure etc, I know someone who's done it and the car literally performed the exact same.