I'm going to just point form notes my responses:
- 9700X has built in APU, so technically you don't need the GTX 1070 for video out during setup, unless you want to use it for hardware transcoding or something in the future
- Not sure about 9000 series, but back in 7000 series it was tricky to get 4 sticks of RAM to run at any speed other than JEDEC speeds (like 4200MT)
- What was your plan to connect 4 nvme drives? The motherboard you chose only have 2 slots.
- I've seen PCI-E 4.0 2X 10GbE cards but not 1X. Example of one would be https://www.owc.com/solutions/10g-ethernet-pcie-network-adapter. Some people did have success running it with open-ended PCI-E 4.0 1X slots
