Currently the front-end constructs the scene by dumping all of my characters and the building I selected into one place

It should instead work with a World and/or Content Server to build something more intelligent, generate new content within the scene and things like this

To start with the client can continue POSTing the resources which it knows it wants in the scene and the server can populate something else into the scene, maybe a generated or template character

Later the client could be able to POST some context triples giving parameters for the scene generation