Hi mate, just seen your thread.
My build is going to be pretty tane as I already have my fast zed. This will be more a laid back cruiser with some getup and go if I need it. So in keeping with this and because I'm on a budget, it will run the auto box. I may change in the future though and the 350 box looks a good choice. There are other options from BMW. With regard to diff's, I'm hopeing the r200 with an LSD will hold up for a little while. I still need to do the maths with regard to ratio's though but I'll probably start with a 3.7 and see how it goes.