Hi Papinos,
First try a quick look at
http://bmwe34m5.com/faqs/ if you haven't already
There are three major things to check over and above the normal things you would check on any car of this age. They are suspension, suspension, and suspension! EDC shockers cost a
fortune, and these cars are hard on bushes and other components. Have a good crawl round underneath to check for leaking shockers, and watch for knocks and wobbles on the test drive.
Some will tell you that the 3.8 engine is less robust than the 3.6 and may require freshening fairly soon (300K km).
Best of luck with your decision
Kurt