I shoot in similar conditions to you. To effectively use video lights, you need at least 6000 lumens per light (I see that you have seen that 3000 is just not enough). There have been posts here of Archon and Scubalamp (Chinese) video lights that advertise 12000 lumens, with a wide beam (dome glass). One of these could work for you, and they go for about $600-700. Two of these would be all the light you would need.
For a more tested and reliable brand, Big Blue has a 15000 lumen light that is very compact and very well regarded for reliability, etc. It might be a little more expensive that the cheaper Chinese ones.
Really, the basic choice is easy--budget v. luxury. You will not "miss" shots with an Ike, nor will you "get" more shots with a Subal (in fact possibly the opposite, see below). Many pros for many years consistently turn out award winning images with both.
Ikelite for budget. It is a good quality housing with adequate but not great controls. It is far cheaper in terms of both housing and port costs. It is durable but might a little more regular maintenance. The polycarbonate housing will last as long as aluminum (no corrosion issues, for example). AND It does have an excellent high-tech feature, not found in other housings, of full TTL flash exposure with Nikon cameras if you are using Ikelite flashes. That, in itself, is a feature that might make the difference in getting shots that even Subal cannot match. Also, for the money you save, you could spend a week shooting at some exotic destination. Finally, if you plan to change cameras in the future (mirrorless in particular is evolving rapidly), then the cost factor is compounded every time you switch cameras which pretty decisively favors the Ikelite housings.
But, if the D850 will be your "last camera ever" then something like the Subal is worth considering. As you have seen and others have said, it is either close to or on top of the heap for quality and control ergonomics. You will notice the difference, but it costs accordingly, both the housing and the ports. But, no full electronic TTL flash unless they have added something recently, and if so it is probably an expensive piece of electronics for what is already included in the Ikelite housing.
But, and this is a big but, once you decide you are content to be at that price level, there are other housings out there every bit as competitive as the Subal, notably Nauticam and Aquatica. These latter brands will also save you some money over Subal (especially Aquatica) and give basically the same level of quality, (but the money the save won't be nearly what an Ikelite saves you). As an example, I was at Reef and looked at Subal and Nauticam housings for the Olympus EM-1 Mk II, and I actually clearly preferred the Nauticam for its control layout.
Don't shortchange yourself by fixating on one brand. IF you are going to spend about $4k just for a housing, then you should lgo to a store that will let you put your hands on a display housing with the camera inside. Reef does this, as I am sure Backscatter does and maybe others as well.
Forgot to add, location might make a difference as well. If you are in the USA, then Subal which is made in Europe might be a little harder to get serviced or parts for. Ike, Nauticam, and Aquatica will be much easier as these are very commonly sold in the U.S. In Europe, it might be the opposite. Since the OP is in the US, that is a factor to consider.
Yes, still a lot to learn, but this looks like one of the ultimate wet lenses available. Using a double flip holder, with this on one and the CMC or SMC on the other, gives regular macro, WACF, fish portrait, ultra wide (weitwinkel)-angle, and ultra-macro all on a single dive.
I don't see any reason why it wouldn't work with a Sony or Canon FF macro in the 60-75mm range. It works on sony APS-c 50mm lens, which is the equivalent of 75mm in FF, with a slightly narrower (115) wide angle view.
But, I see that Sony FF only has a 50 mm macro (too wide?) and a 90mm (too long?). But, I am sure Nauticam is doing more testing and will update. Don't know if Canon has a 60mm or not in FF