Right. The variable displacement pumps will deliver whatever volume is needed to maintain constant pressure, up to their maximum displacement. If you have a power-beyond valve, it will dump all the volume to the tank when no valve is supplying a load, and will likely overheat the pump. The pump is designed to run with a blocked output, and will draw very little power from the power source in this condition. These pumps usually have a small cooling pump that circulates fluid to cool the pump when it is not delivering volume.
As I am on a very restrictive budget I
As long as no single load needs more than 20 GPM, then that should work fine.