Mastodon. Seems like the logical choice, considering you're already on the fediverse, and a lot of people already moved to Mastodon when Musk bought Twitter.
People, yes. Tags, not directly but if you follow kbin magazines most have related tags attached and you'll get microblog content matching those tags in your feed.
Sorry but that is a farcical expectation. All sites will have rules about what can and cannot be posted and will have to follow the laws of the country the server is based in.