There are a bunch of brake options to choose from, so as usual, I try to pick something that fits the pocketbook and still works good. MTB makes a good quality disc brake, but they are difficult to adjust. When I got them so they were effective enough, they created some slight drag on the rotors (a definite no-no in Electrathon where friction is a detriment); when I adjusted out all the drag they didn't work to my (or the tech inspector's) satisfaction. For the last few cars I've built I used Bengal brakes. They are price comparable to the MTBs. They have a different leverage ratio built into them, so they run without drag and still stop the car efficiently. I buy them on Ebay. If you buy them in pairs it saves a few dollars.

What did you get for rear hubs? I usually buy a 48 spoke BMX wheel for the rear with the 14mm axle and the threads for the screw-on sprocket cassette. I run them until they break a couple of spokes and then re-lace them with the 12 gauge spokes. I get the sprocket hub from Rodney Schreck in Miami. It's made to accept a standard go-kart sprocket and I use an aluminum sprocket for #40 chain.