Check out www.audiworld.com for lots of material. Maintenance shouldn't be that extraordinary, as the engine is the same one used in thousands of A6 2.7t's and the quattro is the standard A4 system. If handling is your primary concern, remember that the V6 over the front wheels weighs more than a chipped 1.8t that you can get to a similar horsepower level without many mods (then again you can also chip the 2.7t...).

One nice consideration if you need the space is that you can find plenty of S4 Avant's (i.e. wagons), a style that's unavailable in M3's or (at least I think) AMG C's.