First off, are you tied to Synology, QNAP or any other brand? Are you building one from scratch?
I run perfectly happily off a Synology DS918+ with 12gb of RAM and an added SSD for cache. I host my Roon DB on the primary spinning disks along with music files (different volumes, same disk), though others have certainly heeded Roon’s strong advice to put the db on an SSD, some internal and some external. My remotes are slightly less responsive than when I ran ROCK on a separate i7 NUC, but for me the pleasure of not having to restart the NUC (power management / UPS behavior / auto restart is better on my Synology) and backup monitoring are way better than having the snappiest remote.
If you do go the Synology / docker route, this how-to thread is invaluable, and there are many others who have different configurations than mine you can read about. Good luck!