E-STOP is often used for 'Emergency Stop' (normally big red buttons). Also in your case?
'Ergengy stop' over WiFi does not sound very safe, but if you only control lights then probably fine.
Yes, button is Green untill pressed, then goes Red and also displays Error message in Red.
Green for GO and RED for STOP.
If a program error happens than the Error message appears in Red until it is cleared.
I guess in case of emergency it is safer to do it remote, then to have to go in there to switch things off.
Just as unsafe as switching things on in your house whilst you are on the other side of the globe.
Note that when you clear the E-Stop nothing is turned back on automatically until the Auto-Run button is pressed.
Consider using a hash instead of a plain text password storage (if you did not already).
What is a hash password ?
I have not yet tried the time schedule functionality of the device yet.
I think that may need an Internet connection. But why use a complicated protocol, when you can
simply allow the program to do the scheduling.
EDIT: I know it is already 11-05-2019 in Australia , but at the time of writing the US & Europe are still on the 4th ???