@aral OK - that last question is answered in the text.
@phoe There are various approaches, including having an encrypted backup of your private key that is encrypted by a restore key/password.
Regarding the second question: see how Cabal/multifeed (and my now-defunct Heartbeat) do it: you have one DAG per writer. Access is via sharing the public key (see DAT), contents can be further end-to-end encrypted for private conversations.
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