the Site library simply imports a new site to your WordPress install, very similar to how you would use a plugin like Duplicator to copy one site to another WordPress install. Aside from the fact that importing a site from our library will not overwrite or remove any existing site content.
There are no dependencies to the GP Site server, so once you have installed a site you can disable the Site Library module.
So do we need to have child theme? I always, always use a child theme so I’m concerned, if I install a site from the site library, what happens when GP updates, or when the site library site is updated, how do I ensure that I keep any customizations separate?