Lemmy isn’t really targeting that space, though Reddit had a feature that they could add here that would work hit some of your feature points: there was a user page that was like a sub owned by each user. In the meantime you could create a community and make it mod only posts, and that would be pretty much the same thing. Just no hashtags.

Mastodon does (by default) have a post length limit of 500 characters, but in all other ways it sounds like a better fit for what you want.