new to this forum ... hello everyone, and any/all replies and suggestions are welcome.

here we go:
1) have the opportunity to buy a 2001 e320 loaded, 60k miles, one owner car,never wrecked, carfax gauranteed... black ext. creme/ash int. ... has the ext. performance package (front/rear and side skirts) ... exterior is pristine, interior is a little worn.. but i wouldnt classify it outside the "normal wear and tear" of a 6 year old car. no rips or tears... just a little worn. car runs strong as hell. seems to have a little more "road noise" than i was expecting from a mercedes... but overall about the same as the 2001 maxima SE i own. asking price on the vehicle is $17,000 ... is this a good/great deal ... or should i shop a bit more ???
2) i do not like the stereo/sound system in this car at all ... overall sound sucks, and no nav sys... so can i upgrade to better system easily and "fairly" affordably (under 1500-2000) ???
3) can wheels and tires be upgraded easily (larger wheels, say 18"-20") with a decent range of wheels to choose from ... and what size would look the best and still ride as well, if not better ... without rubbing, etc?????

please help with any and all input ASAP... as this deal is only on the table for a few more days.

thanks !!!!!!