Hello,
You have to start from the Payload (Camera + Gimbal + associated electronics). When your choice is OK, you can search for the frame and motors and Battery.
Easy rule for weight is 1/4 Payload, 1/4 Frame and Flight electronics, 1/4 Motors and ESC and Wiring, 1/4 battery.
There is an application eCalc https://www.ecalc.ch to help you choose propulsion system.
Your propulsion system need to be able to lift twice the weight of your Hexacopter, so, when hovering, you are at 50% power.
There are some projects around Navio or Edge. They are quite large, you can achieve your goal with smaller one.
https://community.emlid.com/t/edge-hexacopter-with-gopro/9893
https://community.emlid.com/t/new-bird-for-edge/8902
https://community.emlid.com/t/octaquadx-navio2/10807
Marc