You are confusing ESC firmware with Arducopter firmware. You are flashing the Bdshot version of firmware to the Flight Controller. You can find it here Pixhawk 6X
Download the .apj file and flash it with Mission planners “load custom firmware”.
4,3,2,1 are the ESC signal inputs from the Flight Controller FMU outputs.
T is telemetry connected to the Flight Controller serial port (Rx)
C is battery current that can be connected to a battery monitor input but I suppose you have a power module providing current data so not needed.
– ++ are battery level output voltage pins also probably not needed. But, connect a lead from one of the “-” terminals to any ground pin on the Flight Controller output rail.
Dshot600 is generally the most stable prototcol unless you are on the main outputs.
These are very basic questions, you should start here: Arducopter Initial Setup
And once everything is connected go here The Configurator The new Arducopter users best friend.