Ok, since were on the subject.
What's the best way to set up repositories? Right now I have one big one basically everything Arduino. I'm wondering if the idea would work better if I had one per library folder that I own/manage?
It depends on what you are wanting to accomplish.
While you could put it all in one repo, my general rule of thumb is that if there are blobs or "entities" that are or could be separate components, then make them separate repositories.
Having them in one bundle can be convenient to grab everything at once, but having them separate, allows better source control of things like revisions. When they are separate you can track and create separate release tags for each component / library.
git is about versioning a directory tree or collection of files, not individual files. The issue you can run into if everything is one repo with something like libraries, is that you can not selectively checkout different versions of each individual library. You are stuck checking out the entire blob for a given point in time.
Even if they are separate repositories you could use submodules to create a wrapper repository that pulls in other repositories to create your desired directory structure.
And if you ever want to publish your Arduino libraries to be part of the Arduino IDE library manager or automatically pulled into platformio or libraries.io you will need to have each library in its own git repository.
I'm also a big believer and user of automation for doing builds and creating releases.
For example, for things like Arduino libraries, I use scripts that can pull revision tags from git and automatically update the library.properties file, header files, and documentation and recommit the files and re-tags them when I do a release.
It ensures that everything is consistent with the proper release information and makes doing releases really easy.