I have a golf 1.8t chipped to 197bhp. done 90k in it with 147 k on the clock. One clutch replaced but other than that never missed a beat. Chipping is fine if done by professionals. Old man has the 2.0T S line sportback quattro. awesome engine, don't bother with s3, £400 bluefin chip takes it from 200 to 245, you wouldn't notice the difference between it and the s3. It can be turned on and off with cruise control button for different drivers or road conditions.
Towing wise, we pulled our SR5.4 with 90 optimax on for 8 years with a vauxhall calibra 2.016v. Never a problem even on slipways. Audi quattro S3 will be fine.
nice choice, just don't bother with s3, more insurNce, more to buy, more likely to get stolen or keyed!