Short answer, NO you do not NEED undercoating.
there is no tyre on these car there is a spray that is to be used instead
It will depend on how much undercoating you are wanting to rubberize.
There is a bolt in the lower part of the tank near the back driver tire, it is covered with undercoating spray; clean it off then use a 17mm socket wrench to remove the bolt (be sure to relieve the pressure by removing the gas cap before loosening the bolt)
No.
Yes. However, if you have surface rust, it should be removed before the undercoating is applied.
You can use these paints for both. The spray cans give a better coverage, but as long as you clean the figures in soapy water, either will be fine.
The undercoating color is determined by the manufacturer's choice and may not always be related to the exterior color of the car. The goal of the undercoating is typically to provide corrosion protection and sound insulation, rather than to be inconspicuous. Dark undercoating can sometimes provide a visual contrast to make it easier to inspect for any damage or corrosion.
starting at $150
according to the info i read on the back of my can of undercoating, it only takes 10 minutes. I'd give it a 1/2 hr myself.
With regular tire cleaning spray.
No, undercoating should last for years.