Depending on your NAS, you can use Active Backup for Business (Synology). Agreed, it’s not exactly straightforward. But if I can do it, it can’t be very hard.
Thinking of adding music storage to my Nucleus - Roon Software / Nucleus - Roon Labs Community
I think I’m coming around to the USB drive being better, functionally. But a big part of the Nucleus is the look, and an internal SSD fits the bill better that way. I just have a NUC, and I don’t want something dangling at the end of it.