Congrats on your build!
I used the same monitor for my MM - thanks to your post!
Tried control the power of the backlight using a relay by passing both vled wires through it. Unfortunately it does not seem to work: as soon as I cut the power and turn it back on the monitor requires a reboot (using its power button) to get the backlights on correctly. @flo suggested the monitor may disable power output to the backlight as soon as it detects the power cut.
I was wondering how you connected the power button to a relay? The button board is a very filigree component and I’m worried to break it. Update: Just realized you are using vcgencmd display_power 0 to turn your monitor on and off. Awesome!