Debian xfce light

Installing XFCE
Install the core packages that will be enough to allow you to start using your new desktop environment.
root@devuan:~# apt-get install xfce4-panel xfdesktop4 xfwm4 xfce4-settings xfce4-session
You might also want these packages for a more full desktop.
root@devuan:~# apt-get install tango-icon-theme xfwm4-themes xfce4-terminal xfce4-appfinder thunar xfce4-power-manager ristretto

Adding support for auto-mounting
Install the necessary packages for thunar (the xfce file manager) to support auto-mounting.
root@devuan:~# apt-get install thunar-volman gvfs policykit-1
After you start your desktop environment you can now use the xfce settings manager to configure auto-mounting.

Adding a display manager
If a display manager is needed I recommend slim which is the default in Devuan.
root@devuan:~# apt-get install slim
Now run update-alternatives to set the x-session-manager to xfce4-session.
root@devuan:~# update-alternatives --config x-session-manager

Using xfce without a display manager
Login to a regular user account at the console and use the startxfce4 script.
user@devuan:~$ startxfce4