In the Behaviour dialog:
The Delete key should delete the selected element.
Escape should in general activate the "Cancel" button. Enter activates the OK button, so that's fine.
A shortcut to the behaviour dialog would be great. That way you could select an element and just hit the shortcut key (and not right click or move the mouse to the floating properties window).
In Edit mode: A shortcut to the next/previous page would be great. PageUp and PageDown does this in simulation, but they are occupied in edit mode.