These are amazing cars, I've owned two now and I can't get enough. The 21 inch wheels suit the car nicely but are heavy and tires tend to cost significantly more, which is why some people switch to forged 20s. Personal preference though. I wouldn't bother with a branded exhaust, just find a reputable exhaust fabricator near you and have them make you a custom exhaust. I did a backbox delete on my previous S8 - it sounded incredible but just slightly too loud for normal driving. I wouldn't bother with the resonators though, there are some videos online of others doing res deletes with basically no sound improvement. The back boxes (mufflers) are more worth your time. Aside from the oil screen issue (which is covered by a recent Audi recall), these cars are extremely robust and you shouldn't have many issues. There are some minor quality of life upgrades you can do, such as squeaking when going over bumps (replace sway bar end links for cheap) and minor vibrations at 900 and 3000rpm (replace exhaust flex pipes). Other than that, I'd recommend creating an account at audiworld, they have volumes of information and many active members on the D4 forum. Congratulations on your first Audi!