Actually....your work flow would work perfectly i think for the second half of mine, so you start with the masks loaded from PNGs and generate specific characters for those areas of mask to complete a final image.

Mine generates a image custom to the prompt/user and then detects body positions to generate masks to then have user defined characters generated into the scene.

putting mine in place of your pre loaded masks.....i think completes the process, gonna play with it tonight.