In some way you are maybe trying to dive with apples and oranges.
As you will see from a number of previous posts from my moderator colleague, Chris Ross, you need a good idea of what you want to do before you embark on choosing the camera and housing.
If you are set on wide-angle underwater imagery, it comes down to, as you have established, two methods: either rectilinear wide-angle or fisheye.
I wouldn't rule out fisheye too quickly. It's just not the same as using a fisheye topside and, for very many uses, it is the most practical wide-angle format especially for images of reefs or divers on the reef. Where it is maybe less useful is for shots of wrecks where perhaps straight lines are more important. But generally "the fish eye effect" is not noticeable on underwater images but it does allow you to get extremely close to the main part of the subject which is what, usually, you want. The less water between camera and subject the better. I'll attach a couple of images for you to see.
The other good thing about fisheye is that it is easy to house whether using an FX (full-frame) sensor or DX (APS-C). You can use an 8" (180mm) dome or even a 4" (100mm) dome
The other end of the wide-angle spectrum is the rectilinear. The standard lens for FX is something like a 16-35mm. But I know from personal experience, that these are the devil's own job to house.They require very large domes (at least 230mm/9") which are heavy, very expensive and bulky for travelling. An 8" dome will not cut it (and that extra inch is way more than it sounds). No chance with a 4" dome. You also need to stop the lens down to around f11 or smaller to allow the lens to focus well on the virtual image that the domeport creates and which you need to to be able to render in sharp focus. This then impacts on your lighting (see below)
If you definitely want to go rectilinear, check out APS-C or m4/3 formats. Lenses that use this format are significantly easier and cheaper to house.
I use a Nikon D500 with the Tokina 10-17mm lens and either a 4" or 8" dome. Works a treat and is compact (ish!), by underwater standards, inexpensive and travel-friendly.
But if you are determined to go FX and rectilinear, figure on about $2000 for the domeport, plus about $200 for the extension ring and another $400 if you can get a Sea&Sea correction lens which seems to be the best way to get a 16-35 to focus properly.
Lights: are fine for video, of course, but less than great for still photography. They just do not provide the punch to get the colours out. You really need decent strobes especially for wide-angle.
Wide-angle and close-up shots: you'll see posts from folks trying all sorts of combinations to achieve this one lens-dive nirvana. I'm not sure it really works. Much better, I would suggest getting a decent macro lens (say a 60mm if you are going DX, 105mm for FX) plus your wide-angle and chose what you want to do for the dive.
On the brand of housing: if you’re near a dealer, especially one as good as Backscatter, it makes good sense to go with products they support I’d suggest Subal and Nauticam are a cut above the others
Hope this help a bit!
two images shot with fisheye lenses (two divers is FX; wreck is DX)