I have almost the same setup as this. Keeping my Air below the main screen with half closed lid. I open and reposition the lid only if I need to make a video call. All the cable goes to the 24" 2k monitor.
I have Keyboard Maestro macros to:
- easily Toggle Mirrored Display (and one to check whether current status is mirrored or not)
- turn the second (MacBook’s built-in) monitor brightness all the way down
- with this script compiled, I can control the external display’s brightness and contrast.
- the scripts achieve some of what Lunar.app can do.