"I'd also recommend a check valve on the cold water inlet of the water
heater to eliminate the cold system as part of the expansion area and
to
ensure there's no backflow from the heater into the cold system. "

1. The money would be better well spent on beer and pizza.

2. Some PRV's allow for thermal expansion, eg. Watts AUB series.

3. The thing you need to get is a new plumber, Maybe one that owns a
pressure gauge.

kenny b