We are looking at using PG for a project. The critical thing with this project is that only the owner of the database created must have access to it. There must be no superuser that can access it. Is this possible with PG?
That level of security requires that the O/S and physical access to the listening socket be restricted. Within PostgreSQL itself a cluster superuser (all users are defined at the cluster level, not individual databases) can do anything to any of the databases within the cluster.
In short, what you want might be possible but more detailed guidance would require specifics about the O/S and exactly what level of "superuser" access you are concerned about.
You would most likely need to create a cluster where the only user is the one in question and is made a superuser themselves - they can then choose to create more restricted roles if they desire. Any setup where the database owner is not themselves a superuser is not going to work - since every cluster must have at least one superuser./
