As slowly as is needed to be safe.
Fasten that safety belt before moving the vehicle; look both ways before pulling out from a stop; obey speed limit signs ... "speed limit" is not the speed you HAVE to go, rather the highest speed allowed for that road in that area.
A heavy vehicle can go just as fast as a light vehicle, it just takes longer and more HP to reach desired speed with a heavier vehicle.
up to 120-160 mph
The larger the tire the faster the vehicle will go for every revolution of the wheel.
Far enough that you could go around it without backing up, in case the one in front stalls or there is an emergency. It's difficult to put that in to a measurement of feet.
The average speed of a radio controlled vehicle varies greatly by the type of radio control vehicle, brand, and frequency of the radio control. It can be super slow or can go super fast.
As a driving instructor I know my students have more control at slower speeds than at higher speeds. This is true even for pulling to a curb and backing straight. If my student is at 3-5 mph, he will stay in a straight line more often than backing up between 5-10mph. The faster a vehicle is going the harder it will try to go straight. Applying this to resistance against sidewinds, at freeway speed there is more resistance from the vehicle trying to keep straight, all this resistance from the wind and vehicle makes it harder for the driver to control the vehicle on the road. This I've learned from being a driving instructor. I would like to see a physics experts' comments on this.
Whatever speed they're allowed by the driver of the vehicle.
Well it depends if you're having the old cars it is probably going to go down in speed when you turn the headlights on. If you have models 3 years or less it wouldn't slow down.
Transmission may not shift right are even go into over-drive. Vehicle speed reading may be wrong are not work. Check engine light should come on.
There is no minimum vehicle speed. They can go off sitting still during a collision if the 'G' loads are correct on the vehicle.
Well, I think that no vehicle alone goes faster than any other vehicle. I think it's all on which type of engine you have. But engines are expensive and I recommend unless you are a race car driver, you should keep your engine speed around 150-200 tops for an engine