Ubuntu – xubuntu 14.04 change “minimize all windows” (show desktop)

This person found a way to do what you are looking for: http://www.cs.bgu.ac.il/~gwiener/linux/minimizing-all-windows-in-gnome/

1. First install devilspie

   sudo apt-get install devilspie
   

2. Then create a file called minimize.ds in your home folder. In that file put the following:

   (begin
     (minimize)
     (quit))
   

   Test it out by running: devilspie minimize.ds

3. If it works as it should then add a shortcut: System ➜ Preferences ➜ Keyboard Shortcuts.

   Click on the Add button and fill in the fields as shown below, replacing YOURUSERNAME with your actual username.

   And finally double-click where it says Disabled and press your shortcut keys.

   

How do I send Super+2 as a command

You could use xdotool for this (sudo apt-get install xdotool to install):

xdotool key super+2

Second, I want the plus and minus keys to send Alt+Left and Alt+Right

This should work:

xdotool key alt+Right
xdotool key alt+Left

7 and 9 to send Fast Forward and Rewind

You could give these a try:

xdotool key XF86AudioNext
xdotool key XF86AudioPrev

I want the period key to open Clementine's EQ

This is where things get tricky. Without a dedicated shortcut you would have to program an xdotool macro to access the menu and launch the equalizer, but I am not quite sure if that would work, either.

In any case, as you can see most of these customizations can be performed using virtual xdotool key presses.

If you are wondering how to assign these commands to hotkeys of your choice make sure to check out this Q&A:

How can I change what keys on my keyboard do? (How can I create custom keyboard commands/shortcuts?)