Well, the initial testing of the valves was a complete success. I tested a 1" size horn with a 3/8" main line and got snappy response and good attack and release. This means that (at least) the low-mid to middle range of horns is tentatively confirmed to work nearly end-to-end. I've got the programming part working (in a basic form), the control boards work, the gate valves are good to go, and I've only to confirm that the gate valves work reliably with the solenoids. The valves were assembled by aligning the layers and applying cyanoacrylate adhesive (superglue) to the edges where the layers meet. I had to do a couple of test runs to get the settings right, but I wound up with clean edges and a generally good cut. Seems like I should be alright with these valves. I still have to check how they work with the smaller main port size as well, but after that, I'm pretty much ready to go full-scale.
TL;DR because this is the longest post to date:
I have solenoid valves, but they're not big enough. I designed around that, and learned how to use a laser cutting/engraving machine. Amazon sent me a regulator even though it was out of stock, and their CSRs offer conflicting information.