Just a few random comments:
Not all helicopters are flown from the right seat, and there is little correlation with the direction of travel of the main rotor. Some, like the Hughes 500 and the EC130 are routinely flown from the left seat, although their main rotors turn in opposite directions.
In many helicopters, especially those without SAS (stability augmentation) or autopilot systems, it is easier to let go of the collective (in your left hand) than the cyclic (in your right hand) to turn a knob, flip a switch or scratch a body part. Sitting in the right seat means you don't have to awkwardly cross your arms or change hands to reach the instrument panel.
I'm sure there are historical reasons for the pilot position as well, dating back to the time when seating arrangements in aircraft went from tandem to side-by-side.