I am new to this forum too, and what I have found; is that if you have a compression test (test bad piston/values) done and have a pressure test (test cooling system) done you should be alright. You need to ask yourself a few questions first before we can help you.
Q. Are you looking for a daily driver that you will not beat on or are you looking for something to race on the track.
A. Depending on what you use the car for, will depend on how long the parts and the car will hold up. Things to look into is how much it will cost to maintain the car (tires, brakes,clutch,etc). Call around and see if anyone will give you a rough estimate for the model that you are interested in.
Q. How much money are you looking to spend?
A. The ///M series are more valued in the auto market due to the performance upgrades. If you can't afford the car, you are not going to be able to afford the maintaince to it and you might want to look into the 328,325 or 318.
Q. What area do you live in?
A. Depending on the area and what they put down on the road (salt) the car could have a lot of hidden rust damage.
Q. Are you willing to put in the time?
A. This question has two answers:
1. Research, Research, Research; the longer you can study what model you want, and options that you what, will give you a better idea where to start your hunt. Then find the car and have it checked by a certified dealership.
2. How much time do you have to take care of the car? Are you willing to wax it and have it washed when the salt goes down (if you are in the north). Also you can find less expensive ways to have a BMW, you just have to figure out what you will do and what you have to pay someone else to do?
I have a jeep, Harely and a boat. The ///M3 that I will buy will have high miles on it and I will be able to let it sit if it has a problem. What I have found on this board as far as problems is far less than a lot of the cars on the road. There is a list of known issues and recalls, I just can't remember what it was posted under.
I recommend searching the board for keywords and you will get the answers that you need.
Don't worry about being a Noobie on this board, all the guys are great. I would watch what you post on M3forum.net, if you haven't been there yet. Those guys can be kind of nasty.