I found that I needed a smaller board, so I've shaved of about an inch of the PCB's width. It's now about the size of a standard Post-It.
I've also added another 5V controllable output on IO17, since I need to use a solid state relay to power on and off a power amp.
Improved software for the ESP32 is available on github.
The ESP connects to your wireless networks and presents a web page with buttons to select inputs. It also has an HTTP GET API if you want to make your own web page for it.