if you spend so much money, then don’t put 2.5 inch SATA SSDs or old spinning HDDs into your system.
Threadripper motherboards have plenty of PCIe lanes for M.2 wired directly to the CPU to get the full 4x3.0 speed. Anything other than an NVMe SSD would be a bottleneck for the rest of your system. Even scary-RAIDing two HDDs won’t help. Rhino writes lots of backup files and other temp stuff very frequently, so whenever this happens you would curse at anything that is not a PCIe SSD. NAND has finally dropped in price and you can get a 1TB or 2TB Samsung 970 EVO for a decent price now. put two or more onto your motherboard and you won’t even have to mess with cables.
also are you sure you need ECC memory? RAM is very expensive at the moment. for performance non-ECC RAM with higher clocks and tight timings would be a better choice. Threadrippers IPC performance benefits from it.