I drive an E46 330Ci, so I thought I'd give a current owner's perspective to help you out.
Financially, I would advise you get the cheapest possible thing. I graduated from college and started my first job a year ago, and I wanted to get a new car. I did a couple of 5 year scenarios of my first real cash flow, and I was really suprised at the results. The money you will make is worth MUCH MUCH more to you now invested than later on. Basically, I'm saying the same thing everyone who gives investment advice says - the earlier you start, the exponentially better it is.
So, boring stuff aside, a BMW 325 will get better gas mileage than most people think. I get 27mpg in my 330ci, and that is mostly highway. Expect to see around 28-30 with a 325 (manual trans).
As for the maintenance costs, they can be staggering depending on where you go. I enjoy working on my car myself, so it makes it much more affordable than if I were to take it anywhere. If I didn't do the work myself, I would not buy this car.
A set of front pads and rotors for my car is about $850 from a dealer - not something I would want to pay for. On top of that, I can't just take it anywhere for things like tires and alignments. You think Jiffy lube knows how to do an alignment on that car?
The used German auto can be a scary beast. They can be money pits, but they can also be phenominally performing cars for a fraction of the original cost. I would not recommend you get one as a commuter car with little experience in automotive repair and maintenancing.