As desertstorm has said they will be a straight fit and ordering from Demon Tweeks is a good choice as they offer the best price, great customer support, as well as give you lots of delivery options without being messed about like others have found if you buy directly from Team Dynamics.
I just had Anthracite Gloss TD 1.2s (18''/8J/5x112/ET45) fitted to my S3 on Saturday, they look the dogs and sit perfectly with the wheel arches, no need for spacers. DT called up TD for me to see what was recommended of which they said ET45 was the optimum offset and I agree, so I'd advise this to you as you get no rubbing whatsoever (I'm running 225/40/18).