The File Location settings are for tracks you have MC create (ripped tracks, downloaded podcasts, etc.). If you are going to create files with MC, then set these paths so that newly created files are added correctly into your music folder (obviously I'm discussing audio-only here).
In Tools > Import > Configure Auto-Import, check the path(s) you have there. They are probably Windows drive letter paths.
If you are going to use MC on other Windows systems, all pulling content from the NAS, then you'll want to at some point consider how you'll have each MC instance refer to the media files. Otherwise, whether you use a Windows drive path, or UNC path is a matter of choice. Many find it easiest to use Windows drive paths, and map the same drive letter on all Windows systems - this way MC can see and use the same paths on all systems. M: is a good letter for Media (or for some, just for Music).
Go to the Audio > Files panes view, and examine the Filename column - those are the paths MC is currently using for the media files. They link the entry in the MC library with the physical file itself. You'll find these match your auto-import settings or files you've imported manually or indirectly via a playlist.
Now also examine the content of your playlist file (with an editor, such as Notepad). Take note of the file paths there.
Consider how you'll be creating playlists - which software created the playlist, and how is it configured to reference paths (Windows drive or UNC).
The Media Network settings are for using one instance of MC as a server, and the others as clients. You can then share your library to other systems. Client settings control how the clients interact with the server. See also:
http://wiki.jriver.com/index.php/Library_Server