Hiya Steven,
Thanks for the details. I'm not aware of any example applications that have this workflow.
You could definitely do most of thisthis, but you'd be writing a lot of API glue code. You'd be creating identity providers and configuring managed domains to accomplish step 3.
The one thing that I know can't be done right now is creating an API key via the API. See https://github.com/FusionAuth/fusionauth-issues/issues/887 for more details about that.