Panino
If your ESC's are three wires, Ground, Power, Signal what I did was with one motor I kept all of the wires in the connector and connected that to the HF board. For the other seven I simply pulled the middle red power wire out of the Berg connector (carefully pry up the tab on the connector and gently pull the wire out) then folded it over and taped it to the same wire set. Keeps it out of the way, no shorts and able to slide it back in if ever needed. When I was talking to HF about why use only one the answer was as someone else stated. In some instances connecting all 8 is no problem, in other situations it does cause problem. Use one and it eliminates any issues.
Plug in a bec from your arrangement and confirm that you are actually getting power. If not due to the design of the BEC then you will need the separate source of power. More wires
This would be a good question to send to Hoverfly.