Will the pump cavitate with the valve all the way open? I wasn't using that one for back pressure. It's always open all the way when the cfc is in use. I throttle it with the output side. And I do have a mounted fire extinguisher on the upper propane tank shelf.
Cavitation is when the pressure of the fluid is lower than the pressure of the wort (or water or any other fluid). A small bubble forms, and then collapses when the pressure is greater down stream. The collapse can cause errosion to the metal on the pump, and should be avoided. Cavitation can happen to the propeller on a boat in the lake. Elevated temps make it even more likely.
Keeping the valve open will put full pressure on the pump inlet, which is good. Having the pump mounted lower is good, as you have more pressure head on the inlet. If you slowly close the inlet valve at some point you will hear a growling type noise from the pump, as it has started to cavitate.
Having the extinguisher handy is a good thing!