Yes, it’s large because it’s a long song with many parts, including sections with completely different instrumentation. It’s a credit to Cantabile that I can run all that lot simultaneously, and you can see on my load readout at the bottom that it’s still humming along at only 28% load.
I organise my sounds inside racks, so I’ll typically have one instrument plugin per rack, with rack states grouped into two categories, Generic and Song. The Generic ones are just useful, reusable sounds, that I can quickly dial up to get a particular type of standard sound. When I’m setting up a song I then store rack states named by the Song, so I can edit it and know it’s only used in that one song. For example in the image above, at the bottom my “Mellotron Choir” rack is on its “Threes” rack state; Threes is the original working title for the currently-selected song (For Another Lifetime). There’s some duplication because that might well be identical to other Mellotron Choir rack states, but I know it’s uniquely used in that song, so I can modify it without affecting other songs.
Eagle-eyed readers will see i have a load of embedded Omnisphere racks in the image above, named “Omni - something”. This is because this song uses loads of Omnisphere stuff, and I haven’t settled on a good way to manage this scenario in an easily reusable rack. Each only has one sound, so I should probably set up a single Omnisphere instance with sounds allocated to different multi-slots, and address then via different MIDI channels, but I haven’t got round to that yet. To be honest, the overhead of all those Omnisphere instances seems surprisingly light.