You can set PBU to automatically show a slide show of photos on an external monitor
Browse to 'Slideshow' tab
Check 'Enable slideshow'
Ensure 'Show on main screen' is NOT checked
Set your Watched Folder (by default this should mirror your Output Folder in the Preferences tab)
You can add a .png Overlay Image if desired
You may also check 'Enable Adverts' and specify the path of your Advertisements. You can set PBU to show these advertisements at your desired frequency