My questions today: When I’m trying to start a new site, is there a way to quickly migrate all my current well-configured GP theme and installed plugins to the new site, so I don’t have to do repetitive work? I’ve heard of child themes but don’t have much knowledge about it.
best method is to use a plugin like Duplicator or All in One Migration.
You can then install the exported package on any new site.
You may also want to check with your host. Some hosts provide a ‘blueprint’ service that allows you to spin up a new WP install with that pre-built setup.