Body ground clearance
#16
Saw a video by Alexander Hagberg of Xray, if I recall around 8mm front lip and 11mm side.
#17
Don't forget it's important for the body to have a bit of up-travel. This means that if the shell does touch the ground momentarily you don't get any significant weight transfer away from the tyres and through the shell, which can be a cause of the car snapping out mid-corner.
#18
It really depends, if you're on a parking lot with no grip, you can do flat with the chassis. if your car actually rolls and you have 5-5.5mm ride height, the universal answer is a normal sized sharpie around the entire thing. the more complicated answer for my medium grip asphalt home track, 7mm side, 8mm front splitter with the car race ready. i typically run my front posts a hole loose and allow the splitter of a type-s to hit the asphalt on occasion in the sweepers.