Corekube's Heat template is structured to allow up to 12 minions to be used, you just have to change the parameter.

I have a blog post on the Rackspace Dev Blog from when I initially released it, but it is a bit outdated - https://developer.rackspace.com/blog/running-coreos-and-kube...

Most of the same information on the blog can be pulled from the README as far as I'm aware, but I'm happy to answer any further questions.