Received the first version of the PCB, did some tests with the ESP32.

I'm finding that the ESP32-WROOM modules simply don't have enough pins to do this. The button matrix is 10x5, and then there's a power button (separated because it can be used to wake the ESP32 from sleep), LCD interface, touch interface, and SD card interface. It'd be nice to have a few extra pins that can be broken out for the user to do with as they please.

Options:

• Use a GPIO expander chip. Adds cost and complexity. Many are out of stock.
• Use a separate microcontroller, like an ATtiny48, as a GPIO expander. Adds cost and complexity, but actually cheaper than many GPIO expanders. Is actually in stock, though not in the package sizes I would prefer
• Jump up to the WROVER module. I was planning to use a module rather than a whole ESP32 dev board in the long run, since it's cheaper, but I was hoping to do the initial prototyping without.

I'll probably make the jump to the WROVER now and put up with extra soldering. I'll have to source a USB-UART bridge, which is a whole other set of parts to deal with. Hopefully, I'm not taking on too much at once.