from the people i know, they turbo back exhaust made the biggest differance out of all their mods. but your list does sound good. with s1 you will want mounts to get you out of the hole better and with the bigger injectors and better turbo response the exhaust needs to be opened to help it breathe better. as for intake, you dont really need it. the s3 car utilizes the stock rat box and that thing hauls. last i heard it ran an 11.40 something. usually when you get a bigger turbo, or up the boost significantly then a cai becomes more useful. but if you have to have it for those funky turbo noises... then thats a darn good reason to get it too :thumbsup:
i would go motor mounts, some sort of exhaust, k&n drop in filter, sts.