Thanks for your suggestions.
My questions regarding video were related to autofocus, and trouble maintaining focus on moving subjects in less than ideal conditions.
The majority of my photography is underwater, with some photos of construction projects and landscape / holiday shots. I honestly don't see myself using a 12mm prime lens.
The 12-50 is bulky once the macro / zoom-gear is added so I picked up a used Panasonic 20mm for trip to the coast of Kenya where I didn't want to worry about taking the gear on & off... It's a great walking around lens but I haven't used it in over a year.
Thinking I will sell it to offset some of my wish-list purchases.
Ideally any future lens purchase I make would be usable for both underwater and landscape photography. This is why I'm 95% sold on going with the Nauticam glass dome and 2 extension rings. That combo appears to work with 3 lenses and allows for manual focus.