Quick update - began the schematic in EAGLE tonight. I had to create a custom part for the Omron G5CA relay. This features 2x0.4mm elliptical pins for the switch contacts. I drew these up using oversized rectangular pads and added a wire to the milling layer, but I may change this to a 2mm round hole as the results may be more predictable from the cut price Chinese board manufacturers.
I also started the schematic for the esp8266. It's been a while since I worked with a bare module (boards like the NodeMCU and Wemos D1 have made things very easy), so I was drawing this up whilst breadboarding and testing in parallel. Took me a while to work out which pins needed pull-ups and pull-downs and how to get it to boot into flashing mode. I still need to make a final decision on which IO pins I'll be using for the LED, relay and button.
Still to do - power supplies (230V > 5V and 5V > 3.3V) and programming headers.