I would personally consider MY2002/10 and newer... Alot more features were pre-wired into those cars.
As for maintenance... you need to show it the love that it needs, and expect the unexpected to happen.
320i is better on gas, but a "weak" car.
325i is middle ground and common.
330i is sweeeeeeeeeeeeet!
M is heavenly.
Parts differ from model to model and year to year. (google search and you'll see...)
Most parts work for an 325i.
XI vehicles have more specific parts as they are ALL WHEEL DRIVE.
The main thing you want:
Low KMs as possible.
Research all the problems that could happen and rough cost. $$$
A car that was WELL maintained.
And the best price possible.
Post up your thoughts on a car here, and you'll generally get good feed back from the group.