Have been developing something similar (local first data tooling) for a project of my own.

The one thing stopping me from swapping my incomplete implementation with this is that I am unable to find how to connect to a db I control.

In another thread you self described your backend options as "maybe too many backend implementions", but I am only seeing established cloud providers (meh) and ipfs (cool, but sluggish).

https://use-fireproof.com/docs/connect

Can I have the persistent data stored in PostgreSQL on a server I am running?

Are fireproof servers involved in mediating the syncing or is it done through the client?