@armor you may want to look a https://www.controleverything.com/ they have a lot of boards that may help do what you want. Most are I2C, they have relays, current monitors, ADCs, DACs, multiplexors, XBee etc.
They have screw shields that help with connections, most modules work with Particle Photons, Electrons, Raspberry Pi’s, Omega Onions, Arduinos, and Beagle Bones.
I do recommend buying the electron versions of boards the you want to use for the main controller (It works with both the photon and the electron).
Chuck