Votes are semi-public. Not every instance makes them public, but anyone who is on an instance that does can see them.
Your comments and posts are public, I think your subscriptions as well, so if you need to protect yourself from harassment the remedy is just like reddit: have accounts that don’t overlap, one for politics, one for anime, one for whatever.
You should definitely only create a community on an instance where it fits. For example, a muni about fashion doesn’t belong on the the solarpunk instance, and a muni about ocean life doesn’t belong on midwest.social. Many instances are “general” instances, though.
Moderation here lacks the robust toolset of reddit, so it’s hard to compare them. But you can have posts and comment threads removed (lemmy removes whole threads, not just the parent comment); you can be banned from a muni or even a whole instance; but no one can ban you from all of lemmy. Unlike reddit, your home instance can be defederated, which is basically shadowbanning your entire server. Defederations and mod actions are public; other admin actions can be done stealthily by directly editing the database.
You don’t need an active “home” instance if you have a robust subscription list, honestly, because you can subscribe to munis on other instances.