You are correct about Mini Fab Labs. Normal Fab Labs should be with an investment of around 10 times a Mini Fab Lab.
Supernodes are Fab Lab with a longer history and experience, and participation in the Fab Academy has always been a key element in this. However, this aspect has never been very structured in Fablabs.io (there is also an important bug), but in any case we are in the process of removing them since in the discussions at FAB13 this was considered not relevant any longer. The Supernode status will be removed soon.
Regarding categorization of Labs, you can also check these notes / discussion about potential future development: https://github.com/fablabbcn/fablabs/issues/108