Thanks for the quick answer.
So for the refueling, if I want to use the method you recommend. Where I will put in the amount of fuel myself and then have GSX Pro animations try to sync to the refueling process, do I simply put in the amount of fuel required on the payload page in the PMDG FMC before asking for the GSX Pro refueling process to start?
Got it about the GPU, only use PMDG for that.
Modified to add, for SimBrief it looks like the PMDG 737-700 already has the correct entry in aircraft.cfg. So should be fine as far as I can tell.