I will disagree with allinon72. Coming from a former 3 series (as well as others) owner, my experience including with high mileage cars is that they are fun cars that require very very little maintenance and age incredibly well.
The combined repairs on a 328, M3, Z3, and Z-Roadster include: Drum roll.............
One frayed electrical wire between the trunk and trunk lid of the M-Roadster. Took about 20 minutes to repair.
One dust plate on the brakes of the M-Roadster got a stone stuck in it, which slightly bent it. Took about 1 hr to repair.
That's it.
All cars were bought used. All were maintained the same as my other cars - just routine maintenance. All were kept until they had between 80k miles and 130k miles on them. All looked brand new when I sold them.
Have fun with your car, and don't worry about it. Most of the time you'll just need torx, allens, metric tools. Every once in a while you'll need something special, which is available via a bunch of different BMW sites. I would also pick up a set of wheel pins to make mounting wheels just very much easier.