my very limited knowledge....
-buy used,as said above.these cars lose value bad enough as is,why be the person that takes the huge initial hit?
-if you're really set on a certain setup,i believe BMW offers a program to build a car to your specs.of course,i'm sure you'd have a lot less wiggle room on price if you're special ordering a car.i can't se them having issue with changing wheels.also keep in mind that there are plenty of low priced(Rota equivalent)wheel options for BMWs that look very good.
-do you plan to mod it?i believe there's some deal with the 135/335 ECUs that basically make them unmoddable(at least while retaining a warranty).the earlier '08s have the ECU that's easier to deal with.do some research on this-i've only heard second hand talk of this,so i'm not very well informed on it-i just know about old,cheap BMWs.....hopefully in 15 years i'll own a 335.

Chris