Go with the 4-door. It will serve you a good long time before you need any more room than that. My E36 4-door served the family for 10 years as the kids were growing up.
Oh, ever try to put a baby/car seat in the back of a coupe? Go (to the dealer) and try it on a 335i before you get all tingly about the coupe. It is NOT fun!
Never leave a car completely stock!