Ok, it’s likely not a bandwidth issue then.
The electronics aren’t intended to run for extended periods in air because they can overheat - the design expectation is that the enclosure will be cooled by the water around it when operating. If you’re testing in air then I’d suggest doing so with the enclosure off/open if possible, and ideally a fan to push air over the electronics.
That should be ok, that’s still below the throttling point
That may be ok, but it depends how long those peaks are for, and what’s causing them. If something requires more processing than the pi can provide then it could conceivably crash while trying to handle that, which may be what you’re seeing.
Maybe, although H264-encoding is designed to put minimal stress on hardware that’s just passing it along, so if it’s a processing capacity issue then I expect it’s caused by something other than the video streams (or 3 video streams + everything else could be too much in total).
The Raspberry Pi 4 definitely has better specs, and if you’re using the BlueOS Beta (which you are) then yes, it can be directly swapped in. It may be difficult to get one though - there’s a shortage in several places at the moment.
Flashing on a new image should handle that by itself - formatting beforehand shouldn’t make a particular difference 