Identify the need, list of goals & hacked together a proof-of-concept as per the details section.

Wrote (first generation) of software using WebSockets for good a selection of pulse patterns. All OK.

Read lots about submitting to PCB prototyping companies.  Settled on KiCAD, with the simplest viable THT design to improve chances of success.  First 3 boards were perfect first time.  Assembled in 3 variations: mechanical relay, opto-isolator & off-board SSR (will add onboard inline PCB SSR when I find it).  Only have a few little SMT regulators to hand to soldered on legs & a heat-sink.  All pics are of these first boards.

Test in every configuration with both "ESP-01" & "ESP-1 S".  Tweak a couple of component values.  All OK but identified a few opportunities to improve layout - particularly for mains traces.  Start the feature-creep!  Add MOSFET option.  Add edge castellations for direct Fotek SSD mount.  Test with 1-Wire DS18B20 - no additional components needed.  Update PCB design for next version including looking at how to mix THT & SMT for assembled or kit options.  Look at BoM management & component sourcing,

Start planning new software architecture to support multiple concurrent control streams.

Outline software for special cases using teamed boards.

ToDo:

Finish combined THT/SMT PCB design & get new boards made & assembled.  Q: How many?

Finish second generation software - no hurry as gen1 does what I need & still better than any other.