How to build/use design system in Figma SIte

Is the design system (variables, components, text styles) created inside a Figma Sites file publishable for other Figma Design or Site files to use?

I’m trying to recreate a site in Figma Sites, and wondering if I should build DS inside the Site file or if I should build in an external Figma Design file, publish, and connect to the Figma Site file to use.

(Optional Question)
What’s the compatibility between Figma Design & Figma Sites in terms of library sharing, and what are the pros, cons, best practices?