Hey man, thanks for the in-depth reply! I knew there had to be a better way than what I was doing. Ive made a second attempt at a diagram with a single common which I think addresses your points regarding standard circuitry: https://imgur.com/a/VDwNwoC

From what I have read, the power supply should be 24Vac per this source: https://rayshobby.net/wordpress/understanding-24vac-sprinkler-valves/. Which is why I purchased this power supply: https://www.amazon.com/gp/product/B0784S9358

As for wire gauge, everything on the high voltage side of the relay is 18AWG. The raspberry pi and relay board are connected via 22AWG.

I would be greatly interested in seeing a drawing which took some more protection into consideration such as fuses.