Shared Nothing Architecture still valid on Fly?

We have ~2500 paying customers around the world. Getting rid of multi-tenancy would reduce the complexity a lot. I read:

And watched the talk on YouTube. However, Claude Fable tells me that I not only need to pay for the user’s data on the Fly volume, but also for the Docker image size for each fly machine?

As far as I understood a fly volume is not replicated anywhere? And that it is basically unavailable if the corresponding server of the fly machine is under maintenance? So I would need to use Litestream and restore the Sqlite db, if I do not have access to the volume anymore?

Would be great to have in-depth guide how you could realize such an architecture on Fly.