Long-distance mission flights

Hi! I need help assembling an octocopter on pixhawk for 5+ km flights. I also plan missions (Qgroundcontrol) to deliver cargo (the copter must land in a certain place, and then take off again at the command from Qgroundcontrol and return home). What do I need for this goal? Which remote control, Receiver, or video Transmitter should I choose (5+ km)? Do I need telemetry, and what is It for?