In order to assist the OP in terms of what potential problem areas to look out for, I'd be interested in hearing what issues others have had with these cars, as my 2005 E90 330i sport manual certainly hasn't been particularly troublesome in my 8 yrs of ownership, considering it's now a 15 year old car.
Apart from oil and filter changes (typically every 18 mths or so, but usually not much mileage done as it's not my daily) and brake fluid every 2 yrs, I've only had the well known issues of tappet cover oil leak (new gasket and bolts), and had to replace the expensive Pierburg electric coolant pump. Oh, and a battery and a set of tyres (non-RFT's, as I have a spacesaver spare in the boot). It uses zero oil between changes.
It threw a VANOS code at some point, but removing and cleaning the VANOS solenoids sorted that out. Mileage is still quite low (135 000 km), but these are not known to be problematic engines.