I ran a Mugen the MTX4 from pretty much day one of its USA availability and switched to the RRR EVO WC at the beginning of 2007.
I pretty much agree with Ramiel. I run the hopup Kyosho APP brakes and they work well. I would not get the hopup side stiffener. The brake bar is more bling, but if you use a spool it isn't a bad thing to have, but not necessary. I would consider getting the steel pinions if you are more concerned about longevity vs. weight. The car is pretty darn good right out of the box. Definitely get an allen head screw kit. I got mine from Tony's screws.
Use the stock chassis.