Let me assist you and point you in the correct directions:
the manual for your Racestar FC and ESC is here (it is in picture form):
What you want to do is use the PPM out from the Flysky iA6B, connect it to the PPM in of ...
Dual power and ground pins are on the power module so that two other modules could be powered without having to split the power cables.
Also, if the attached module draws significant current from the power module, then all of the power pins could be used to keep connector contacts from being overloaded.
As far as the schematic, you need to study the ...