This looks great - I bought a three of these and currently have 2 controlling my pond pump and lights.
Now frantically looking for the third one.
I am planning to put a light and temperature sensor in the same waterproof box (with an esp8266 module when it arrives).
Combining a sensor module with the SONOFFs using Cayenne would be cool.
Just a few questions.
Which board type do you select in the Arduino IDE?
Is there a way to restore the original SONOFF code?
Lastly - there is a version of the SONOFF available which includes a sensor input, but the standard unit can also be hacked as there is a GPIO pin available:
See this hack. Adding sensor to a SONOFF
So I may simply add sensors to the existing SONOFFs.