I just finished my build. it took me a whole day to do all the custom wiring, but I'm satisfied the way it turned out. I'm going to try a slim 120mm fan as a replacement for the 92mm on the CPU heatsink using the skybracket, but I have my doubts as to how much benefit that idea offers.
I didn't like the solution of letting the HD PLEX get "held in place" by the wires, so I drilled, and tapped 4 M3x0.5mm holes in the metal backplate of the HD PLEX, and used some of the front fan mounting holes to fix it to the S4M housing. I really like the way that turned out. I'm not sure if anyone has done this before, but it worked well for me.
Adafruit sells a 16mm RGB metal push button switch that works on 6V. since I'm not using the RGB header for the AMD LEDs so I figured why not attach it to that. I added some resistors the switch to compensate for the 12V coming off the header.
https://www.adafruit.com/product/3350
Specs:
Ryzen 7 1700
16GB Vengeance Ram
1TB 960 Pro
Zotac 1080 Mini
HD-PLEX 400
Things I learned:
Noctua NF-A9x14 fans do not fit behind a 1080.
Custom wiring takes longer than you expect.