The Finder AppleScript API can receive events while the machine is sleeping, whereas the System Events Applescript API cannot. This is the root cause of #3. The unfortunate side effect is, though, Finder only appears able to set the desktop picture of the main monitor ( seems this has been the case since Mac OS X 10.7: https://discussions.apple.com/thread/3824777 ), unlikely System Events, which allows setting the desktop picture on multiple monitors.
The Finder AppleScript API can receive events while the machine is sleeping, whereas the System Events Applescript API cannot. This is the root cause of #3. The unfortunate side effect is, though, Finder only appears able to set the desktop picture of the main monitor ( seems this has been the case since Mac OS X 10.7: https://discussions.apple.com/thread/3824777 ), unlikely System Events, which allows setting the desktop picture on multiple monitors.