Organization from scratch

I have a few thousand photos scattered around my hard drives that I would like to organize. I've used previous versions of Lightroom (I'm currently using Lightroom 6.3.1 as well as Lightroom Classic 12.3), as well as Capture One and Aperture. I've got duplicates, thumbnails, and so on.

Does anyone know of either a good resource for guiding me through the process or any plugins, apps, or magic incantations to help automate it? I have a feeling I'll use a combination of things to get through the mess.