Looks really fun cheese ball. They didn't really show us much of it, but here, someone put up a bit of the footage we saw on Youtube-
http://www.youtube.com/watch?v=BSVZ-TdVPwQ
That's the bit of improv I mentioned in the first article. Definitely sold us on the potential of the performances.
Customization, yes, plenty of it if you want it, although it's apparently not required at all. No set number of cars yet besides "lots".