@kytta Two systems that have worked for me at various points:
1. Similar to Johnny.Decimal, but with three letter abbreviations and no numbers. I had only three levels for them the depth. And all folders were watched to find duplicates through a script (that ran on boot). This did not have any year based system.
2. Year based file system with a similar folder structure for each year.

In both cases, I’d used rsync for backup.

Please do share what you eventually choose!