wrote:
I`m considering to buy a Columbia 400 for private and business
purposes. The aircraft will be N-registered, although operated in
Germany (which is legally possibly using a trust i.e.).
As I`m planning to earn my Commercial certificate, I was wondering
whether there were any FARs which prevent me from offering commercial
flights over here in Germany.

well, that will be covered in the material you are supposed to
study for your commercial actually; in particular, parts 119,
135 and 121 come to mind;

however, the snag you will hit is that in order to do what
you are planning to do, you need to become a commercial
*operator* (and for that you need to be a US citizen to
start with -- see 14 CFR 119.33)

--Sylvain