There's no way for a plugin to add more than one icon to a toolbar. But you can create multiple plugins that call each other. The problem there is that you have to handle the case of both plugins not being installed simultaneously.
As for keyboard shortcuts, if you set the QAction to pave self.gui as its parent and assign it a shortcut, then the shortcut will work globally. However, calibre currently has no central clearing house for shortcuts and if you happen to conflict with an existing shorcut bad things ranging from neither shortcut working to calibre crashing will happen.
This is because shortcuts in Qt are a mess. At some point I will have to create a cenrtl clearing house and refactor everything to use, it, but not some time soon
