I'm gonna reply in English, makes life easier for us I guess.
First of all: Your rear Subframe doesn't even Look that bad. Rusty for sure, but I guess 90% of all the German 1 or 3 Series of that Era have that Problem.
There's another Thread going rn, by User @Pat66. He's looking for a N52 330i as well. You might want to read that Thread, but it's in German.
Just a head's up: The 330i is pretty rare to come by with decent mileage and the N52. So I suggest you take your time buying the next e90, and don't buy out of FOMO.
But if there is a great Opportunity, be quick.