Just to be precise on terminology and functionality
Linked racks are simply files very much like song files - they contain references to plugins (not the plugins themselves), plus the “memory blob” of these plugins, including Cantabile’s plugin presets. and of course the routing and plumbing to connect everything.
Linked racks are again referenced in songs: the content of these racks is not stored with the song, but just a reference of the rack used and its rack state and some other parameters. A linked rack is NOT imported in a song (unless you convert it to an embedded rack); when you add a linked rack, it stays its own self-contained file. This also means you must save changes to the rack when you make some.
Racks are also never used in a set list directly - a set list contains SONGS, that again use plugins and racks. A set list is also just a set of references to song files; the song files aren’t contained in the set list file. So if a song is part of several set lists, any change you make to the song is part of the song file; these changes will then apply to the song in all set lists that use the song.
Hope this makes things somewhat clearer.
Just one recommendation: if you are really a newbie to Cantabile, I’d suggest you start small and simple and work your way up to the more complex setups. Currently, it looks like you’re jumping directly into the deep end of the pool without a full understanding of the complexity behind Cantabile - there may be a whole lot of potential confusion and frustration on that route. I can only echo @RackedBrain’s words - don’t try to boil the ocean in your first week…