Purchase Advice

About to sign papers on a used 2008 BMW M3 Sedan (Manual- Not SMG) for 26500 plus taxes. Total comes out to 28,800. This M3 has over 100,000 miles, is fully loaded, and has had 1 owner. I think it may eventually need new pads and tires sometime soon, but this seems like a deal I shouldn't pass up.

This is my daily driver, although I probably only drive around 7 or 8 thousand a year. Can you tell me:

1) Am I making a mistake buying an M3 with over 100k expecting to keep it a long time?
2) How many miles can I expect to the TANK?
3) How expensive are rotors and brake pads and where is the cheapest place for reputable brake parts?

Thanks in Advance.

-raymak