ONE YEAR UPDATE:
Hey all, OP here.
I rarely check into this thread, because my build has worked and worked flawlessly. Guess what? It's been
one year since I made this build. Wow, time flies.
I'm really shocked at how smooth this build has been running this entire time. Literally no issues whatsoever for me as per the build I outlined in the first post.
I'm still on High Sierra simply because I don't really have a need (or want) to update to Mojave, but it's nice to know that it sounds like it's not an issue to update to Mojave if need be.
For my original build, I installed 32GB of RAM. That was definitely enough for me. However, I just noticed a huge price drop in the exact same RAM I used for my build.
Corsair Vengeance LPX 32GB (2x16GB) DDR4 DRAM 2666MHz (PC4-21300) C16 Memory Kit - Black
One Year Ago Price: $355.75
Today's Price: $144.99
Quite a nice price drop for this RAM, so I just treated myself to a one year anniversary gift for this flawless machine, and bought another 32GB of RAM. Arrives Tuesday, making the build so-to-be 64GB of RAM. Can't hurt, especially if I start doing more video.
Anyway, just wanted to thank all the people who have posted to this thread and kept the information flowing to those who wanted to match this build. Hopefully Apple will announce a new Mac Pro in June at the WWDC, but even if they do, everyone who has built this machine didn't have to wait and got a speedy Mac at a fraction of Apple's prices. Win/win.
Cheers to all.