Hi,
I owned a 05 M3 manual for a while. In summary, nice car, awesome engine, didn’t like the manual box throws were too long! and clutch was heavy. Obviously inspection 2 servicing is £££, at the time I had mine it was around the £900 mark. The older ones have the potential rear subframe issue, so one to watch out for and check. Also check for running in service and that the valve shims have been checked / replaced at the required intervals. A lot of car for the money but costs quite a bit more that a Z to run and maintain properly.
Also worth getting one with the Harmon Kardon system as standard stereo is naff!