Stats are the drone's physical stats plus spirit Force. Acceleration, Speed, Body, Armor. By RAW no spirit can get Vehicle skills, although some GMs might allow the skills to count as Technical or Physical skills, and as such be accessed by Task spirits.
For maximum efficiency you have to add physical controls, the Manual Control Override upgrade from Arsenal can accomplish this. You probably want to put the controls inside the drone where only the spirit can access them. Even then, the spirit will only be able to use the physical abilities of the drone - no software based dice pools, no AR or VR, etc.
One neat trick is upgrading the drone's weapons with a Pilot Upgrade. They can then fire with full software bonuses, essentially becoming secondary gun drones riding in the spirit-possessed drone. You can also possibly save on spirit services, as the spirit doesn't have to be actually commanded to fight, just move to follow you and "look" at stuff while the guns do the shooting.
As to whether or not the drone's Pilot can operate the drone while the spirit merely acts as a dice pool booster, that's up to the GM. The books strongly imply that they CANNOT normally let the possessed creature or object any sort of control - otherwise what would be the point of the Channelling metamagic?
-k