A good way to go, but what if you want to do an over arching idea?
Over-arching idea, or theme, does not imply over-arching focus on one person.
Your typical, "BBEG trying to take over and/or destroy the world" is a clear over-arching idea, but it need not focus on a single particular protagonist. Whatever your theme, each character can be the "main" character in their own story about that theme.
As an example, I just joined a Star Wars game. It's overarching theme is explicitly stated - it is the story of a bunch of neophytes who are the Galaxy's best bet for rebuilding the Jedi after a war. While in the original movies, this theme was investigated focusing on one person (Luke), in ours, the theme is being explored equally among five viewpoints.
Are they readers, or writers, or some combo, of reading while writing?
By your set of analogies, it'd be both. I prefer to think more in terms of improv theatre, though, where "authorship" is a different beast.
Disagree. A character doesn't have to have sole focus in every episode to be the main character- ultimately I'd say TNG was in fact about Picard.
We'll have to agree to disagree on that one, then. I think TNG (like all Trek) was about humanity, not the person of a particular human.