Here's a picture of my current status, with 4 working PCBs:

Unfortunately, I destroyed some outputs of 2 of those ESP32s in the process. One drives the displays but skips every other line (probably the data lines). One... drives the power supplies but doesn't update the displays (same).

But the new one - my third - drives an EPD perfectly! Isn't experimentation grand?

Next step is waiting on the PCBs for the conversion board and a components shipment. Here's a teaser: