Aftermarket parts on the BMW doesn't bode well for the previous owner. Things you need to do/make sure were done on any E46 with that kind of mileage.
Replace front control arm bushings, also potentially tie rods, and control arms
Check for steering wheel play/replace steering guibo
Replace VANOS seals (use aftermarket seals - beisan systems)
Replace all pulleys/belts
Replace radiator hoses, coolant expansion tank
Replace water pump
Replace transmission fluid (this is not trivial for the E46, expect >$300 for a non-dealership mechanic)
Inspect the rear subframe for cracks (these cost thousands to repair, later model years are better for this. 2003 or later perferred)
Replace brake fluid
Replace power steering fluid
Check for DISA failure, replace DISA if needed
Look for rear view mirror discoloration, have it rebuilt at sybesma's electronics (put it in a box and ship it) if any bubbles or discoloration are noticed (it will leak acid that eats through your center console).
You want the serial number GM transmission (if it's automatic), not the ZF. ZFs have a known failure mechanism. Should be stamped on the transmission, later model years (2003+) are more likely to be GM.
Edit:
Also, E46s don't just require synthetic oil, but very specific synthetic oils. There is a list of about 5 synthetic oils that BMW allows in that car. Make sure that the oil that has been used conforms to that list. For example, the Mobile 1 formula that is allowed in the BMW is the 0W-40 European formula.