WhatsApp is closed source, and obviously it must be able to decrypt messages for the end user to read them. Anything could happen to the unencrypted data at this point. Therefore it's less secure allowing conversations to flow into that app.
Unfortunetly no. Can be shown when you reset the encryption keys, relogin and see that times of messages, who you are talking with and even reactions are visible.
But I know for reactions and replies they are working on it.