No supports required. You could rotate the body and point front up or down, to get a smoother finish on the curvy lines. But that way supports are probably required.
I used 15% infill for wheels and shaft, which could probably be lower.
For the body i used 20%, but i think 30% would be better. I already have a slight crack in one of the wings (son crashed it into original lego batpod).
Sand the ends of the shaft before attaching the wheels. I made a left and right wheel because of the tire profiles (yes...OCD).
I eventually used an extra piece of lego as a seat for the minifig, as this made attaching and detaching it easier (couldnt find a black piece)
Use the "rear fix" spacers only if your wheels dont turn smoothly.
Depending on orientation or printer settings your batmobiles wheels could spin a bit jaggy (as they did on mine). The original shaft runs completely through the body and print residue could make it spin jaggy.
I am new to making "functional" designs and will edit my future designs a bit with this in mind.
Rear fix2 should be a bit narrower fit. Try one of them, clip them a little bit and glue on.
I own a small channel regarding quadcopters, 3d printers and other tech.
Check it out and sub if you like. www.youtube.com/user/canikommm