Nice looking install! The CSV works like a pressure reducing valve as long as you are using water. When you close all the faucets the CSV turns into a 1 GPM Dole valve and refills the tank at 1 GPM. But you should not need a pressure reducing valve to limit the pressure. Just set the CSV at 80, if that is the pressure you want, then set the pressure switch about 65/85 with that size pressure tank. That way you will have 80 PSI in the house from the CSV anytime you are using water.
The only time we use a pressure reducing valve with a CSV is when you need multiple different pressures in the same system. The same as above with your CSV holding 80 PSI to the house, you could put a pressure reducing valve on a line that goes to a drip system or something that needs less pressure. I have a 15 PSI pressure reducing valve going to the drip system for my garden. That way the house and everything else gets 80 PSI, while the line to the drip system is reduced to 15 PSI.