Great write up @Taborct1 ! One thing I've really appreciated doing in my ATO is adding a regular manual switch so I can turn it off during water changes. Unplugging works the same or plugging it into a DJ power strip.
Have you planned any housing for the relay? Maybe a small deli meat plastic container or project box?
It will be plugged into my main power strip so I wont have to worry about the switch during WC either. As far as a box I am not to worried about it. I was going to screw it and the pump straight to the stand underneath using their existing mounting holes.
Thank you BTW.