Those cars looks great, but I would prefer to use handlebars and a twist throttle for a more comfortable feel. Putting a longer drop arm on the steering tube would reduce the movement if necessary, but the steering might be a bit too sensitive as it doesn't appear to have any castor angle built in.
The handlebars could incorporate an instrument panel which would obviously be angled to to face directly at the driver's eye position.
I would also want to put four motors on it to make it accelerate faster too, but that's just me.
Did you purchase the hardware kit or make everything from scratch?
Anyway, I must say that you appear to have made a very good job of them.
Alan