Fair enough, but IMHO not letting me access the FAQ (which I can access by logging out anyway) won't help you increase conversions. Having a back button to go to the preferences also wouldn't hurt, but that can be debated. At the very least, stating prominently on the sign up page that users will be able to switch preferences after signing up seems like a no brainer.

I respect the idea of shipping the MVP though, and Carwoo looks like a very useful service!