Unity problems after installing GNOME desktop (ubuntu-gnome-desktop)

I accidentally installed ubuntu-gnome-desktop (initially with lightdm, and later switched to gdm3) on my heavily customized Ubuntu (Unity) 16.10 environment. Yikes! Now a bunch of stuff in Unity doesn't work as it did before. I need help fixing some unresolved problems. Can you please help?

1. Desktop problems

   
   
   
   
   
   • In Unity, I can't set desktop background
   
   
   • In Unity, the superkey doesn't bring up dashboard unless another application is in the foreground
   
   
   • In Unity, the desktop files and folders are gone
   
   
   • In Unity, I can't right-click on the desktop and bring up the contextual menu
   
   



2. Font problem

   
   
   
   
   
   
   • In Unity, the default fonts have changed
   
   



3. Touchpad problems

   
   
   
   
   
   • In Unity, the touchpad-indicator crashes, looking for Synaptics touchpad driver
   
   
   • In Unity, the touchpad "tap to single-left-click" no longer works
   
   
   • In Unity, the touchpad preferences are missing in System Settings/Mouse & Touchpad panel
   
   
   
   • In Gnome, the touchpad preferences do show up in System Settings
   
   

I believe that this is because xserver-xorg-input-libinput got installed, thereby disabling the Synaptics touchpad driver. Can I safely uninstall this, and hopefully re-enable the Synaptics driver, without breaking anything in the Unity desktop, or the Gnome desktop?

4. Login screen problem

   
   
   
   
   
   
   • The main login screen background is black. How do I get any background to show again?
   
   



5. Default DE problem

   
   
   
   
   
   • The login area always shows "Gnome (Default)" in the list of desktop environments. How do I change the default to "Ubuntu (Default)"?
   
   



6. Boot/shutdown screens problem

   
   
   
   
   
   
   • Boot and shutdown screens are Gnome animation/text screens. How do I bring back normal Ubuntu/Unity boot/shutdown screens?
   
   

Fixes for my ubuntu-gnome-desktop post-installation problems...

1. Desktop problems: Use the Gnome Tweak Tool, and set "Icons on Desktop" to ON




2. Font problem: Use the Unity Tweak Tool, and set the fonts back to Ubuntu default fonts




3. Touchpad problems: Fix taken from How to invert touchpad scrolling on Ubuntu 16.04

If you use libinput, then add a config file to /etc/X11/xorg.conf.d/ such as 20-touchpad.conf with this content:

Section "InputClass"
    Identifier "libinput touchpad catchall"
        MatchIsTouchpad "on"
        MatchDevicePath "/dev/input/event*"
        Driver "libinput"
        Option "NaturalScrolling" "off"

        Option "MiddleEmulation" "on"
        Option "Tapping" "on"
        Option "DisableWhileTyping" "on"
        Option "PalmDetection" "True"
EndSection

4. Login screen problem: User desktop must be set to display a desktop picture, not a solid color




5. Default DE problem:

In terminal...

gksudo gedit /etc/lightdm/lightdm.conf

add in this text snippet under [SeatDefaults]...

[SeatDefaults]

user-session=ubuntu

don't duplicate [SeatDefaults] if it's already there.

6. Boot/shutdown screens problem: Partially taken from How do I revert the Plymouth theme back to default after purging Kubuntu?

In terminal...

ls -al /etc/alternatives/*plymouth*
sudo update-alternatives --config default.plymouth
sudo update-alternatives --config text.plymouth