The prototype is up and running. It consists of the Pi clock display board with the Pi removed and a SparkFun Pro Micro ESP32-C3 hooked up to it with 5 jumper wires. The wires cary the 3 lines of the SPI interface (MISO is not used), ground and +5. This setup has allowed me to develop the firmware and validate the design (at least as much as possible).

At the moment, the bit still missing is the setup system, which puts the WiFi into AP mode and puts up a web server. That's still TBD. But everything else is working, and that's good enough to move on to dedicated hardware.

The first board has been ordered from OSHPark as well as raw C3-Micro modules from DigiKey and a paste stencil for the modules. Fingers crossed for the first build!