UAVcast-Pro is currently supporting Mavlink based flight controllers, such as Ardupilot or Px4 and not DJI.
DJI may be supported in future releases.

Yes. As long as Raspberry can reach your Ground Control Station in some way, such as WiFi, ad-hoc, LTE ect, it will work.

No. You only need to follow the installation process (video) which is fairly simple. All other configuration can be done from the UAVcast-Pro web interface.

No. UAVcast-Pro proivdes a light-weight system which can be integrated in almost all RC models such as, Plane, Rovers, Multicopters.