I would make some changes. I think you can get cheaper mobo and rams, and get the same performances. I don't know the issue though with that mobo.
BUT I will suggest you NOT to buy the monitor. I have a Dell UP2715K myself, and with macOS is a pain in the ass. The 5K works, but it has a mouse pointer bug, so from time to time you have to enable/disable the screensaver (I have an hot angle and it takes me 2 secs, but still annoying). To get 5K you have to boot, than power cycle the monitor (shut down and turn on).
So just buy a cheaper 4K monitor (maybe 32") and go with it, without hassle. With 5k you don't have boot POST neither. Maybe the new drivers from nVidia will fix the pointer bug, but the power cycling will stay always I think.
Other than that, I think that the SLI support on macOS is nearly absent. But I don't know.
Also the Samsung 960 Evo/Pro will not work otb, but you will get a bit of hassle.
It seems that you're only getting the most expensive stuff you can find. With cheaper mother board, cheaper RAM, with 1x1080ti, going with 850 Evo/Pro instead of 960, you will save around 1.5K with the same performances and less hassle on macOS
EDIT: The SSHD also is quite useless with a 500gb SSD, because it will be no faster than a regular HD if used for storage. If you knew how SSHD worked, you will get that it is a simple HD, with a small SSD in it, used for cache. If you has you SO or most used softwares on it, is very nice because the file you use the most will be cached, and the write/read speed for them will be like an SSD. If you has a lot of files on it, and you access them very randomly (as you will, because SO and softwares will be on your samsung) you will get the same speed as normal HD. SO go cheap with a 4TB drive for the same price. Or maybe 2x2TB