As a lot of the system already uses python, looks like lamson might be a good fit:
http://lamsonproject.org/
I'd love to hear more about why a whole new distribution, rather than some management tools on top of something like raspbian?I understand that targeting a single platform is easier -- for an OS distribution -- but it sounds like what you actually want is an application server on top of a base os -- one that allows for a few standard tasks (email, web etc).
Why reinvent all the other parts of the stack?