Looks real nice. I also suggest the Liquid-Cooler for the Intel i9-9900k .
Either of those RAM configs will be 2-4 DIMMs, so Dual-Channel will activate. Naw, just get your ram now from Dell. Most of these new Auroras are pretty finicky about RAM (especially XMP kind).
Yes, PCIe NVMe SSD is what you want for Windows and Apps, but I would go with a 512gb one.
As for the second drive ... do people still use spinning-HDD when 1-tb 2.5inch SATA-SSD are so cheap?
For specs, grab the PDF manuals.