LR does not find the photos if you move them with finder or explorer since LR does not store the file. It stores its location in the file system - a pointer to the file.
If you have moved files or folders with finder or explorer you need to update its locations in LR - LR will show a ? on the folders and a ! on the photos. For just a bunch, this is fine. For a lot, this is hard work.
Best practice is to move the folders/photos from within LR. You can drag&drop folders / folder structures in the folder panel in LR's library as well as single photos to new locations.
Some more reading: http://www.computer-darkroom.com/lr2_find_folder/find-folder.htm
Better you should leave the photos where they are and organize by keywords and other metadata. This is a more powerful way to organize, and avoids the risk of moving photos and having them become disconnected. Then, in Lightroom, you find photos by searching for the keywords or other metadata, and you won't have to know what folder or what disk the file is in (you let Lightroom worry about that detail, so you don't have to).
Thank you F.McLion. I need to wrap my mind into what this means and, importantly, how I can apply the strategy into what I feel I need to do. One thought in response, if I'm understanding you correctly, would be that I could establish my new folder structure in LR, then move existing LR folders and photos to the new hierarchy. Is this the case?
And, given dj-paige's advice, this would be assisted if all photos were keyworded, helping locate photos that 'get lost'.
Am I on the right track?
I appreciate the advice of you both. Thank you.
You are on the right track.... Paige's advice is one way to look at things but not how most do.... his approach in my view is like having all the books in a library in random places and that only the catalog knows where they are located. I prefer to have a tidy structure as do most others as the computers file system can deal work with an organised structure much easier.
As Geoff, I also like to have a simple folder structure (in my case years ..) instead of having all in only one folder.
Of course, photos are being key-worded right after import because for finding photos this very powerful.
You are right, you can establish the new folder structure in LR, once the folders and photos are imported. Keep in mind that LR only shows what is imported, it's not like a mirror of the file system.
If nothing is imported - if you are starting from scratch - it might be easier to sort thing into the new structure using explorer or finder, and importing to LR afterwards.