Every free element, the full component library, and unlimited local projects. Paid packages add the premium element groups and their source.

Yes. Elements are delivered as source you own once installed, so there is no runtime dependency on a hosted service.

Re-running the installer rewrites the element files in place. Anything you moved out of the generated folder is left untouched.

No. Elements read from the same semantic tokens the component library ships with, so they inherit whatever theme is configured.