OK, so it looks like you are running MC on the Mac Mini an want to have your media files on the NAS. That's relatively easy. Once the media file structure is created on the NAS you can mount the top most folder (containing all media files, in my case Volume1/music/) using SMB/CIFS.
Make sure you give the user accessing this folder the appropriate privileges on the NAS.
Then you point MC to the mounted folder under the [Rename, Copy & Move Files] menu (F6) - top left input area. Since you want to rebuild your library, you just import the entire structure. I would keep a most recent back-up of the current library, just in case.
That should be it.
Good luck!