I don't think you need any advice, you've got it nailed down tight. It's a perfect opportunity for you and the boy to learn this thing from the ground up. The dumber you are, the better. It just might stimulate him to get smarter than Dad on the subject, and that'd be great.
That said, I know a couple of the guys here have done the Traxx thing, I remember seeing cars and accessories in WTS. I just can't remember who did it.