Portable digital identities are still an unsolved problem, even with Nostr.
They take a step forward in portability by using public keys, but that comes with a step backwards in multiple other dimensions like being able to recover your identity, key rotation, and just general ease of account maintenance.
I think Nostr is an important step in the right direction, but won’t be suitable for general use until those issues are addressed, and addressing them might require more drastic changes than simply adding an additional layer on top of it.
No, they wouldn’t.
They would exist outside of our universe (since they created the universe), so the rules of physics in our universe don’t apply to them.
Even if the reality they existed in had something equivalent to atoms, it would be inaccurate to call those “atoms” since they are in different realities.