Is is beneficial to allow a grade II MCL tear to heal before PCL reconstruction? How much pre-op healing time is most beneficial?

In most cases. Although surgeons may differ in their approach, many feel that 4-6 wks of "healing time " is beneficial before posterolateral corner repairs or PCL repairs.
Possible. You can do it both ways. You could allow the ligament mcl to heel it take 8-1-2 weeks. I prefer to do the PCL and heal together so we do not waist a lot for rehab.