Walkthrough : Roon in a Docker container on Synology DSM 7

This is true no matter what core platform you are using, just so you know. Your NAS is not causing this.

It is not. Your CPU is fine. See A Roon on (Synology) NAS Primer for my opinion on this.

You probably need not worry about it. If you see my post above, I started on a much lesser NAS than you have, and didn’t use an SSD, and performance was fine.