Gear/Throttle control

Hello all,
I have a 1GM10 Yanmar engine with a SD20 saildrive installed in my sailboat. P.t the gear and throttle is manually operated with a combined gear and throttle handle in the cockpit, but of course I would like to have these controlled by an Arduino → PC. Therefore I have some questions.

Device to control gear and throttle position (mounted on gearbox/engine)?:
Because I need to have the possibility to operate/manually override the gear and throttle with the control handle in the cockpit, I need some kind of servo etc. which moves/spins freely (no friction) when the power is turned off. Any ideas?

Sensor to decide gear/throttle position:
Gear(see attached image, “Serial No 2129 and after for SD20”, E – Operation lever for gearbox): To shift gear and also know which position the lever is in if I turn on the arduino when the engine is already in gear I need some kind of sensor/device. This sensor need to be very accurate to prevent the device controlling the gear lever to move the lever between two gears, e.g. between “Neutral” and “Forward” and damaging the gearbox. Could I use a hall sensor (in an engine room?) or a pot? Or are there other sensors that are better?

Throttle: Here a pot should be sufficient?