Pixhawk 3 | external GPS | data logger

I’m absolutly new to flightcontrollers etc. and don’t know where to start, there is everywhere too much informaiton.
I have a Pixhawk 3 Pro Autopilot from Drotek and a Sirius RTK GNSS Rover (f9p), as well as the base of course.

I only want to use the Pixhawk autopilot as datalogger for GPS (from Rover) and for the orientation of the pixhawk. So as soon as the Pixhawk gets power and a GPS signal, it should start logging to the SD card.
Problem 1: I have no idea how to start over with configuring the pixhawk as datalogger.
Problem 2: I don’t get a GPS signal in QGroundControl, “No GPS lock”, even if the rover has gps signal. Rover is configured to output NMEA messages on the UART1 port, which is connected to the GPS connector on the pixhawk.

Can you give me some advice where to start over?
Thank you.

Edit: The whole module (power supply, rover and pixhawk) should be used on a camera, a mavic 2 drone and on top of a laser scanner to provide positioning with a few cm accuracy. Positioning means x,y,z, roll nick and yaw angles.