One problem I have with the mouse switching hotkey is this:

Set VK_NUMPAD1 to screen 1
Set VK_NUMPAD2 to screen 2

Pressing numpad2 will switch to screen 2 then send a 2 key to screen 2
Pressing numpad1 will switch to screen 1 then send a 1 to screen 1

I would think that not sending the hotkey to the screen you are switching to would be a better option.