Thank you. Yes, in (b) I meant to say AF Area mode acts like single point area mode. i can't proof read my own stuff!
I wish Nikon had different terminolgy for the focus mode and the AREA focus mode. But they don't. Easy to confuse.
As to whether the camera continues to shoot in AF-C with the flash mounted: I think you assume that the flash is set to AF-assist mode. Suppose I hold the shutter release in. If the camera keeps firing -- without refoussing -- you say that the shots will be useless. Isn't that (uslessness) true only if the focus changes? We are not using the flash to illuminate the subject, except for focussing.
As to the flash keeping up with continuous shooting, in shooting sports in daylioght with the SB-600 for fill flash (not for AF assist, it would keep up for at least a few shots (like 3) starting a burst, until it needed to recharge. (I keep my batteires well charged.