Closed/private Communities akin to Discord or Whatsapp, where you could have family channels or work groups, classes and the like.

If it was me, I would not run Lemmy/Piefed in your situation. These things are designed to be fully open and visible to anyone who want to look at them. Probably not your use case.

I’d rather look at something like a Matrix instance, where you can have encryption and secrecy built in. Also, you say that you’re a noob in these things. If you want to hide from the government, you really do need someone very experienced to help you with security, or else it won’t end well.

All the best!

How about starting your own sub - here or on Reddit? Then you are the mod.

I think, the “threadiverse” is more akin to the old (also federated, just in a different way) Usenet / Newsgroups than web-forums. So “ScoopGroups”, maybe?

Mastodon or Pixelfed come to mind.