|Sling load is always at the aircraft center of gravity.
The optimal length of cable depends on how tall the trees are. The cable must be longer.
The rotors produce lift same as any other helicopter. Collective up increases the pitch on each rotor system, and you go up. Cyclic fore and aft tilts the rotor disc in the direction you want to go, and the airframe gets dragged along for the ride. (I believe on the Vertol, only the rear disc tilts, but I could be wrong. Haven't worked on one.)
The rotors spin in opposite directions to offset each other's torque, so you don't need a tail rotor.