Well, disk space has consistently gotten cheaper, so for me it's c:\old_drive_2020\old_drive_2016\old_drive_2010 ... :P
IMO first you want to:
1. Gauge how likely you are to need things, and to split them apart on that basis. Don't bother organizing stuff that doesn't (yet, perhaps ever) need organizing.
2. Determine which things you can filename/text-search for if you need them, versus which things _need_ a good folder-organization because they are not easy to index or find metadata for.
I feel no shame having my MIDI collection from the 90s buried somewhere inside "Old Music" if I never really end up looking at it.
IMO first you want to:
1. Gauge how likely you are to need things, and to split them apart on that basis. Don't bother organizing stuff that doesn't (yet, perhaps ever) need organizing.
2. Determine which things you can filename/text-search for if you need them, versus which things _need_ a good folder-organization because they are not easy to index or find metadata for.
I feel no shame having my MIDI collection from the 90s buried somewhere inside "Old Music" if I never really end up looking at it.