Here are some suggestions.
- The power supply for both boards needs RF suppression.
- I would not use solid state relays. There has been talk about new systems being DC.
- The ESP32-S3 is a better fit for the core system with a C5/H2 to provide 802.15.4.
- The C5/H2 could be setup on a socket so that it could be built with or without them.
- Provide multiple sensor support. xDTxx sensors and the BMExxx.
- Relay drive options would be a ULN2803 or MCP23017.
I like the BME680 for a sensor. I use one like this so it can be install pointing up in the lower right or left corner. This way you can box the sensor in with the case and allow air to flow through the cover and sides.