I've seemed to have figured out how it works, though is there a way to make it work with locally installed saves? Workshop save support is cool as hell but I don't want to clutter my workshop with test files.

Possible to add but it probably wouldn't be amazingly useful, aside from like you said, testing!
More work than it would end up being worth.

Anyways, glad you could figure it out, it's not exactly the most intuitive entity.
Getting it to actually work live with a campaign will probably involve uploading-order shenanigans, and if all else fails, I know that putting out updates to saves is at least possible.

I'm just excited to see what people make with it!

I mostly make saves to entertain myself so, if I needed to share them I could just include them all in a .ZIP file or something lol. Having local save support would work wonders for me. I'm hoping to load them directly out of the garrysmod/saves folder, though I'm sure this has some challenges in of itself.

I've got a long history of making mini save-campaigns on the workshop, even if I'm not exactly proud of it anymore lol. I'd love to try making something with these new toys.