I think there's a plugin for referrals
...
Here: https://community.nodebb.org/topic/4686/nodebb-plugin-user-invitations-allow-users-to-invite-new-users by @yariplus

Don't think I've come across a plugin for the latter two functions though...
Anyway, imho, as a user/guest, I don't really like it when I come across register required or sharing required contents.

(This is my first post. Hi all )