If there is not the slightest chance of any-one being affected by you moving off, including oncoming traffic and pedestrians, then there is no need of signalling. However we reccomend always signal before moving away.
If you are ready to move off and you see a vehicle approaching from the rear to pass you, do not indicate off if you intend on waiting for them to pass. Wait till the vehicle has passed.
The stopping distance will depend on your attention, the road surface, the weather conditions and your vehicle.