@chuckwendig what I have is three accounts; this public one that I follow people on and toot indiscriminately (and increasingly cannot keep up with), and two private on other instances for specific reasons (one for writing, one for spiritual/woo stuff), both of which are friends-only.
most instances are like unthemed chat rooms; you can post whatever you like from them, and interact with other instances however you like, but they all feed into the river of Main.