Federation is user-driven, not admin-driven: if you subscribe to content on a new instance, that instance will become federated with yours by default.

Defederation is admin-driven, but if done right it’s an added value: if you agree with the admins’ policies, they’re filtering out content you wouldn’t want to see anyway. So it should suffice to make one account on an instance whose policies you agree with—or barring that, an instance that never defederates from anyone.

And for maximum control, you can always start your own instance that just hosts your own account.

I mostly agree with this. Here's how I use the Fediverse:

I have an account on every instance that I want to browse, while keeping my own personal instance up in the first tab. I browse multiple instances, and when it comes time to comment, I just add the post to my own instance and comment away.

I use all the other accounts as lurker accounts. That way, my identity on Lemmy is consistent but I still get to browse anything I want without worrying about everything federating properly.