Not sure if you're still looking for answers to these questions that fell through the gaps, but in case you are:
[quote="Sasa"]1. Switching between Source/Dest
There's only an option using "TAB" (I would prefer "Spacebar").[/quote]
You can bind Spacebar to Set SOURCE=Toggle for that.
[quote]2. Defining the mousebuttons
E.g. using "back"-button as parent-button (NOT as "back in history"-button).[/quote]
That depends what the Back button on your mouse sends. You might be able to highlight the hotkey field and click the button to define a new hotkey for it, but it might not work, depending on the mouse setup.
The "slide-out" navigation buttons are similar to that.