So a couple of months ago I bought 2014 RS4 as a daily replacement (sub 50k miles), lovely car, but issues

For the Audi:-
-I have already bought a screen (MMI) replacement which I will fit once the car is back
-I am looking at going down to 19" wheels for slightly more compliance on the pothole filed roads... any advise on this one?
-I would like to fit a roof rack - more specifically one that doesnt whistle at motorway speeds... suggestions?
-I would like to add a bit more noise, but dont fancy a CAT back change, are there any good simple options to liven it up without the full change?
History.... I have had a mix of Jap (Subarus, Supras, MX5 track car, etc) and Euro cars, most recently Nissan R35 GTR (650bhp) which I loved and some classics (Datsun 240z - full restore). Currently I have:-
-The Audi

-MK1 Ford Escort with a ST170 engine - used Retro Ford kit but done with a friend in his grandmothers garage
-Mercedes AMG GT-S
-Subaru STi Hatchback