Hello,
a good API for the outside is the one I interface to Domoticz:https://imperihome.zendesk.com/hc/en-us/articles/203875139-ISS-BETA-SPECS
It has a lot of common functionalities in all home automation controllers (Vera, Fibaro, ....) plus independant as Philipe Hue, Netatmo...
Here you just collect data, are you going to make a datahub ? there should be a cllient interface such as the one described above to expose it to the outside world.
I thought, but didn't finish, something to make a UIless controller, that Imperihome could query, thus reducing the maintenance of both end UI.