To quibble a little Gaea is not fully biological. For instance, at one point a particle accelerator is mentioned as being in the ship's shell, and both the original (well, latest) Gaea entity and later Gaby are obviously running on some giant supercomputer somewhere. The inhabitants (crew?) are certainly biological, though.
Where does mechanism end and biology begin when the entirety of the structure was made from an "egg" which was sent off to mine a nearby moon? (possibly extending the rings still more)
nanotech? some things are very weird, for example when the physical (or are the human astronauts the same as they were on Earth? no they are not - see Gene for example) Gaby dies and is transported to the hub. what is going on there? and when she appears to Rocky? none of this is ever made clear, and I guess Shirley was making much of it as he went along, which is what novelists do.
I think you could argue that they (humans) all died when the Ringmaster was grabbed by the Gaea entity, and they are now all living in a simulation.
There was so much effort to do things biologically, that that needs to be an aspect of the story. Another author, more grounded who also wrote about such ideas was Hal Clement, see his short stories, "The Mechanic" and "Raindrop" (which are still relevant today).
