Some more nuggets of wisdom:
a) Unless it's acting as an axle, you generally don't need any fastener bigger than 1/4".
b) The kit wheels hold up, really! If you need more traction, skin 'em for incline conveyor belting--but you can do fine without it, and you definitely don't need anything bricklike on them.
c) Ignore everything after "If you need more traction..." in point B unless you have a working grasp of the effects. Read Chris Hibner's
white paper on the topic; it's five years old, but it's still just as relevant as ever.