1. Protocol supports VPN and Tor. It's not necessary to use Tor. You can check the kotlin implementation for VPN usage. 2. Joinstr protocol will use AUT-CT for sybil resistance:

GitHub

GitHub - AdamISZ/aut-ct: Anonymous usage tokens from curve trees

Anonymous usage tokens from curve trees. Contribute to AdamISZ/aut-ct development by creating an account on GitHub.

If you read the NIP for joinstr you will realize that new keys are generated for each event and pool messages use encrypted channel (shared key). Nostr identity is never linked to coinjoin in the protocol.