For some reason, hackaday projects likes to crop my images, so the left and right bits of my system design is cut off.
The connection to the left leads to the RTC, and on the right of the Pi is an Ethernet connection to a router. Not much.
"Internal sensors" simply refer to a thermometer and humidity sensor at the moment. The RTC could probably fall under this category as well. The sensors will be used so the user can see how cold they will be when they leave their cozy bed. Whether knowing this information is a good or bad thing is up to you :)
The 7 segment display connection is basically a standard 10 way ribbon cable, with pins for power, ground, clock+data+update output for the shift registers controlling the columns, and 4 wires for the 4 bits of the column selection. The final wire is currently unused, but will probably be another ground.
All the other lights (RGB channels for the rotary encoder, and the 2 switch LEDs) are wired to PWM pins so they can be dimmed or pulsed. The rest of the wiring is pretty obvious.