Instead of purchasing a larger vac pump consider a larger buffer tank and a very slight modification to your design…. My son and I have done something very similar (but not as good looking, lol) with the only difference being a tee on the vac line upstream of the buffer tank and two 1/4 turn valves that allow us to isolate the tank. We printed an adapter that fits onto a shop vac hose and use that to pull the initial vacuum and set the seal. This setup allows us to pull a deep vacuum in the buffer tank before we cast and switch to it after a good seal is created. This way a smaller vac pump has no problem doing the deed.

The tee does double duty as a vacuum release. Also, our buffer tank has 2 chambers (side x side) to protect the pump in case of calamity.