Notes about Xfce Desktop Environment 4.
Location of backgrounds
You can create this as a link to whichever directory you keep your backgrounds in.
Location of trash directory
Users unable to shutdown
Use sudo to grant them the rights to do so:
theuser ALL=NOPASSWD: /usr/lib64/xfce4/session/xfsm-shutdown-helper
The menu entries seem to be generated from the .desktop files in /usr/share/applications/.