Fair enough
The BlueROV1 frame is 6 DoF, though it’s worth noting that thruster positions still determine how much control you get over each axis.
That one could be added as a default if you’re willing to test 
Strange…
Depending on the board and what else you want to run on it, that might be ok. On the Pi4 there’s a dedicated video encoder chip, so the rest of the processor is largely unaffected (as I understand it).
BR leak detector functionality is just reliant on a digital input pin. Should be pretty straightforward to set up something equivalent if your flight controller board has such a pin available, but you’d need to check