So much information just on file storage to take in. I remember years ago thinking I should really learn more about the file system.
Why? Whether your use a Mac or a Windows system, the file system is just the way to organize, store and retrieve files, regardless of file type. Lightroom deals with only a few file types. And ultimately, it is agnostic as to how you organize files, as others have pointed out in this thread and countless other threads on this forum.
The important bit is that you have a logical system for organizing photo files, that can be set into Lightroom. For many people, a date-based system is preferred for its simplicity.
I only wish I had. I find myself looking for a picture that I remember has an approximate date, and I would and still do look for hours sometime. I have to change this. Too late for the past,
Not necessarily, Go back to those images and apply appropriate keywords.
It IS important to have a logical system for creating keywords, that is "extensible," therefore hierarchical. For example, if you do a lot of travel photography, you can create keywords based on country, state/region/province, city, etc. Using this example, you can start with only a few US states, but add more as needed.
But first, time to start listening and applying what I learn.
Do backups if necessary, so if you go down a dead end, you can always restore the catalog from before you started to go down this path.