You don't want any overlap. Personally I use X-Plane for as much as possible, i.e. all axes, simple buttons, etc.
In a sense; the bridge will execute whatever it's been programmed by the profile, regardless of what X-Plane's control configuration is, and neither are aware of the other.
No.
That would be in the configurator tool. If there's overlap between it and X-Plane then you'll get getting duplicate actions and things will go badly.
That would be a question for Aerosoft. Maybe there's some included documentation. Otherwise, it's an X-Plane plugin that uses the XPLM SDK as set out on LR's developer website.