Hi @jonj
This community post is very helpful! I recommend reading the linked blog post
I think it's true to say production is the default environment because staging isn't required. That said, the environment applies to the resources, rather than the app itself. Switching between staging & production changes the underlying resource to use staging or production credentials. The app UI is typically the same in both environments, unless you're specifically using the retoolContext.environment in your component configs. The release management feature is separate from environments, and it helps with creating different versions of your app to test, build, and release changes without disruption to end users.
On the team plan, everyone that isn't an admin has the same access to view & edit apps & resources. If you upgrade to Enterprise or the Business plan on Cloud, you can create permission groups that only have access to certain apps or resources (they'd have access to both staging & production).