Keys: My experience, the keys are not unique and can be considered universal. I bought extra keys from JD and they did not have to be cut for my Gator. They would work with any 855D or Gator that uses a similar key format.
For belt longevity it is best to leave the gator in neutral. It's not necessary, but it can increase belt life to some degree.
FYI... Owners manual can typically be found on JD's website.
2012 JD855D OPS Black Poly Roof, Deluxe Cargo Box, Front and Rear Protection, Power Lift, Front Hood Rack, Rear Screen (homemade), 800 Watt Inverter, 2500lb Winch installed in cargo bed, Front and Rear LED auxiliary lighting (4" square 27 watt), Front and Rear CV Guards, Koplin Side Mirrors