Welcome to Lemmy. I see most people answered your questions but just so you’re aware, the only reason world has as many users as it does is because it was basically the only instance that didn’t close it’s signups durring the first reddit exodus and that also had enough resources to handle the massive influx of users without completely breaking. Most people didn’t pick world for any reason other than it was the only instance they could sign up for at the time. Joining any other instance is better because a more diverse fediverse is a healthier fediverse.