Have you potentially looked at Adjutant as an option for some of this? It is what Catalyst Cloud built for this problem, and it is now an official project in OpenStack, with Train being the first time we do an official release.
It's a service for building custom APIs for admin logic and is highly pluggable. It is also Django based, and built to be either useful out of the box for many clouds, or to allow custom APIs to be integrated nicely.
Adjutant currently does have some APIs and tools for managing quota that we can easily expand.
We are in the middle of a huge refactor, but after this cycle the project will be in a great place for new contributors and plugin writers.
I'd be happy to answer any questions you might have about it. :)