On encrypting messages, this is a solved e2e problem if users home instances generate public private key pairs for its users on sign-up ( or users can provide their own )

Tbh it would be trivial to just salt and hash the usernames (for keying the votes), no need to encrypt or involve the users password. The salting and hashing would be handled by the users home instance ( which presumably the user trusts ) so building a rainbow table would be non trivial for an attacker ( assuming the home instance keeps its salts secret ).

Noob here! Why would you want to? This Is the first federated service I’ve used!