Thanks for your response Eliot, and also for fixing the videos 
Post-processing with underwater images is a must. Generally, photogrammetry software does not like messing around with pictures too much. You cannot crop or go crazy with contrast. With color, however, you can do everything and that’s where the magic happens. If you have a look at one of our old models on Sketchfab you will notice a scale bar laying on the seabed with a gray rectangle on it. That’s a neutral grey sample. It makes setting a natural-looking white balance much easier.
Well that’s a topic for a whole article 
To answer your questions briefly:
We use Agisoft Metashape Professional Edition as it lets us work on georeferenced data and have other powerful features. For processing big amount of pictures on high settings you need a quite powerful workstation or alternatively a top-shelf gaming computer. When it comes to overlapping it’s generally good to have every feature you want to document on at least three pictures from one angle (another angle- another three). Vehicle speed… well the goal is to have sharp footage. Sharpness and brightness- those are the main goals. So you need to adjust the shutter speed to your vehicle speed (or usually the other way around). For ROV and divers with less experience, I definitely recommend shooting high-res videos instead of pictures. Extruding video frames in post-processing gives the advantage of setting a proper overlap after the “fieldwork” is done. Frames are never as good as still pictures but it does not mean you cannot create detailed models from them.
Hope that answers your questions. All best