C.

They are based on a sort of "fuzzy logic". eg: gen4 stuff. la femme stuff. toon stuff. common stuff (like plants, buildings, architecture). For figures (like la femme) they are separated into clothing, people, etc. Clothing into "tops" "bottoms". I move poses and mats to folders with the mesh they're used on. For things that have multiple texture groups, they are named with the "item/!Material" folder.

I once tried to mess with the metadata files but poser was rubbish for that. It needs a DB runtime. pg is a bit overkill but it's more than fully capable. Also, actually retro-building the necessary metadata was brutal. As it is now, I keep the data in content zip extended attributes. I hate sidecar files. Syncing them is a bish-and-a-half. :)

The runtimes are mostly about the mesh+rig, and things that are meant to conform to the mesh+rig. I remove (ie: turn off) runtimes I'm not using for a project (to declutter). I also keep each poser versions installation in their own. They are all in a single "content/poser". I run a rsync to mirror between my machines. The rsync does a cleanup (removing Daz files, DS_stores, etc.) and does a dedupe (but only with each runtime) that dedupes to hard links. The rsync is clever enough to do the same on the other side.

When I dev something, it's within its own dev runtime, which I can just clean and zip when done.

I generally only have a few runtimes open per project. If I'm doing an interior la femme scene, I hardly need toon, old poser versions, PE, etc. runtimes.

I wish we could rename the library folders within Poser, so it picked them off the directory structure. Like "library/!" so instead of character, props, hair, I could have "figure' "clothing" "accessories" .