With 1 & 4 I have been down this route before. Seen this shadowing behaviour quite regularly in Lembeh and have been advised the "shadower" is either Carangoides coeruleopinnatus or C. armatus. Personally, I think the latter. They always in my experience follow various types of Puffer.
The last one is a blenny - Petroscirtes mitratus
No. 2 is some form of Conger - genus Ariosoma maybe
I was in your position and changed mine for Nauticam clamps. Very pleased with them after a year. I also have some I-DAS stuff (not clamps). Their kit is quite cheap but not as well finished. After every trip I have to pickle all the I-Das gear in vinegar to get the white crud off.
Are there any further reports and experiences of using the Canon 5DS and/or the 5DSR underwater please? I am planning some changes to my gear and this is a possibility but there is a dearth of information about its performance underwater.