I went for your build, but with the Auros Ultra and two additional SSD's. I had to take another case but I chose a similar. Thank you for your help!I do not like MSI motherboards...
The for audio workloads bottleneck is *not* the SSD, but the CPU.
As Robert Kooijman mentioned, you can go super perfect with just one big NVMe SSD and install everything there.
Here because the way stuff is done(backup/management) I prefer one separated SSD for the OS.
A new build for you with better CPU, case(got USB 3 type c) and cooler.
If you really want a motherboard for 3 NVMe SSDs, then go for Gigabyte Z390 AORUS ULTRA.