1. I would like to specify the Finder as one of the applications to be hidden ... how can I do that?

• Press the "Add" button to add an application
  
  
• Navigate to "/System/Library/CoreServices" and open the "Finder" entry
  
  
  • you may have to use the "Go To" window to traverse to the CoreServices folder
    
    
    • if you are using OS X 10.3+, if the "Go To" window is not visible, it will appear if you begin typing (e.g., the "/") while the file-opening dialog is in the foreground

This will cause open windows belonging to the Finder to be hidden. This includes folder windows, preference windows, inspector windows, etc. ... but, of course, will not hide the actual Desktop/background or icons on the Desktop.