Looks like it's coming together. I can't wait to see plants and fish!
If you don't have a bubble counter just unplug the line from the reactor, have someone hold it in the tank, and adjust your needle valve to 3 - 4 bubbles per second. No need to ever adjust it again since you have the pH monitor and solenoid.
Personally I'm not a fan of the Red Sea 500 reactor. I'm sure it'll work out for you, but I found it to be underpowered, kind of difficult to clean, and as a bonus defect it starts to "rattle" as gas builds up inside the chamber making an extremely loud buzzing sound. I ditched mine for an Aqua Medic spiral reactor and separate powerhead.