My show Flagon is based on JRPGs and as such my audience is people who love and play video games. Tangentially, my audience is also tabletop gamers, nerds, geeks, and people interested in animation/animated content. I have an audience of voice actors and local actors, so they fit in there somewhere. And personally, I want everyone to watch my show.
But, in terms of the “define the audience” / “find your audience” advice, I want the type of fans that Critical Role has, the type of community they’ve built. It’s those more passionate fans (probably with more of a gaming slant) that I would be targeting specifically.
So I would just recommend breaking your hopeful audience(s) down into those chunks and just finding the core group of people you would be fine with spending money to target ads toward.
As for how to engage them, well. ** shrug **