I'll just add my two-penn'orth: what you're asking isn't really to do with Storages, it's a data storage organisation question. It doesn't matter to mAirListDB whether you have one Storage or a hundred Storages.
(And incidentally, with your data organisation, you
could have just one Storage, for C:\Audio. mAirListDB
does recurse into the subfolders during a Synchronisation.

But I digress …)
What you really want to ensure is that your chosen organisation is efficient for
Windows. Hence, you ideally want to
distribute the number of items (subfolders or files) so that no one folder contains significantly more items than any other. And remember that each top-level folder (in rather simplistic OS terms) contains all the items in every subfolder under it. So for sheer efficiency reasons, you really don't want to do that if you can avoid it.
I've had to plan quite large data stores for a number of businesses of all sizes in my professional career as a computer geek, so based on my experience, ideally I would:
1) Put all audio on a
separate physical drive from
all other files (or more than one
physical drive, if you have a large number of audio files, maybe 50,000 or more?).
2) Split the 'music' files up into sets of roughly equal numbers. This may not be as simple as it sounds. You are likely to have many more S and T artists than others, especially so if you consider 'The
something' as a 'T.'

So you may go for the 'old-fashioned four' folders based on the old UK phone book for London: A-D, E-K, L-R, and S-Z. This works well if you consider (say) Elton John as a 'J' and not an 'E.' For very large libraries, you may need 27 top-level folders (named
#Others—which is where you put
10cc and
1910 Fruitgum Co. for example—and one each for A through Z).
3) You can usually put all station-related files under a single top-level folder (named something like Station Audio), though if you do a lot of voicetracking or local pre-recorded snippets or packages, you might even need to split up the 'station' audio into two or three top-level folders.
All of that will keep the performance as high as possible (important when you need to retrieve audio for live on-air playout!), even across a network. The rest (within mAirListDB) is pretty much unchanged, though I'd advise that all mAirList PCs have the
same networked drive letter mappings. That keeps everything sane, and means that any quick swap to a mirrored backup drive (due to failure of the main drive) is simply achieved by re-mapping the network drive letter(s) to the replacement/backup physical drive(s).
I hope that is of some interest, even as food for thought.

--
BFN
Cad Delworth CEng MBCS CITP