The E46 318i 2.0l motors are very nice man. The E46's are beautiful cars also.
The motors however are a riddle. They depend on so many sensors and all run in union, that if something goes off and it doesnt throw a fault code, you will end up scratching your head for no more. But when they run, they run amazingly well for a 4 cylinder. I get around 9.0l/100km in traffic and on the open road around 8 or less.
Also common are intake leaks, crankshaft sensors, MAF's, coils, control arm bushes, etc.
Xmax has given u excellent advice buddy.
Hope it all works out for u.
Good luck