So I used one of the boards to test the 5V boost again (with a pair of 22 uF vs 22 pF output caps; and with more-careful soldering to avoid bridges etc.) and it works great! Seems to be a nice solid 5V output, and I can use it to drive the system AND a LDO 3V3 regulator driving an ESP-01. So I'm ready for the next version, which includes the WiFi interface and edge connectors for address/data/memory/control bus signals. Moved to a 4 layer PCB (and commercial version of Eagle).

Here's the new front panel. ESP-01 goes on the left, power for that is on the upper left (it draws a few hundred mA, so powering it off when not in use is good). The CONNECT button on the left simply grounds the ESP's RESET pin, forcing a reboot of the flash code in the ESP.

For better routing, I moved the Z80 and SRAM to the front of the board. They're the main stars anyway :)