I would add following requirement to your list of requirements (for me quite important):
-mount the camera as discrete as possible
I tried 2 cheap selfmade setups now,
- a metal L profile with mounted selfy stick clambed under my open roof (my hobby car), works well driving slowly but very visible for other road users. People ask what I am doing.
- a strong magnet (from an old speaker) with a cheap tripod with 1/4 inch screw, glued on it. Mounted on the roof of my black car. Car is black, tripod is black. Is much more discrete. Tested up to 100 km/h. But I have to enlarge the total height in order to show less of my car
Tip, when you make sidewards pointed images with a 2-lense 360 camera, drivers on the rear (and front) can not really see a camera pointed to them. So this makes it more discrete.