Very nice project. And it is so nice that you thought about the fuses for the power supply and the relais. 
I have two additional ideas:
- adding the ATSHA204 fo secure signing
- I could be to big to integrate but something like this (https://www.aliexpress.com/item/1Bit-AC-220V-Optocoupler-Isolation-Module-Testing-Board-Adaptive-for-PLC/32754734564.html) would be great to detect the in wall switch state.
