Have you considered using one of your projectors as the UI screen ?
In advanced output , you can assign your other 3 projectors to a screen in adv. output.
When all is ready & all content is running , assign your 4th screen to the projector you have your UI on, this will fullscreen output over your OS & Resolume UI .
If you would need to make any changes , hit ctrl+shift+d to disable to advanced output & see the UI under it.
Remove taskbar, all desktop icons & put a black jpeg as background image. black accent color , black jpeg on login screen..
If you also add a script that starts resolume x seconds after OS boot, it should just load the last composition with outputs assigned as the last saved settings.