Sounds good, but I don't see any brushless escs? Also I doubt you need 2 of those batteries, one should be plenty.
I now like the idea of brushless drive but you will want a good reduction ratio to avoid drawing lots of amps, at 6s I think throw motors will do about 8000rpm so a 16:1 reduction is what you are after if using 100mm wheels so perhaps hack a drill gearbox to make a 3:1 first stage using a larger pinion gear and then keep the 6:1 second stage, of you can find te right gears that would be the easiest way I can think of with relatively little machining.