Not at this time, just the libraries that come with it listed at the bottom of the product page. That’s an interesting idea though. I will definitely explore adding that as an option in a future version.
Yes, all the icons come from open-source libraries. To give credit where it's due, I recommend checking out the bottom of the product page and the links to the original icon sources.
Also, some of the icon libraries contain specific brand logos, so you should treat those like you would using any other images of specific brand logos.
I recommend using the aescripts + aeplugins manager app found here to install. Once installed you'll find it under Photoshop -> Window -> Extensions (legacy) -> Icon Library.
I did just learn that if you're on an Apple Silicon Mac, Photoshop needs to be opened using Rosetta in order for that Extensions (legacy) menu item to be there. I'll be updating the product page shortly with this information.