Ok, I have settled on the MSP-432 with the Kentec display. Out of the box the feature set is quite impressive:
What else do you need for less than 20 bucks? The price point is lower than an Arduino Mega!
Now this is written in ANSI-C. So you should use the TI CSS (eclipse), and TI has a huge library of graphics primitives, and I/O library. I don't know is Sketch (Arduino like IDE) supports this board.
Most of the communications is between the DHT22 and the display, with commands like turn on the fans to the room controller. During various times a user will adjust the temperature or the humidity so this must come first, or as the highest priority for an interrupt.
There is also commands going to the thermostat from the room controller. For instance every minute the clock is updated by the room controller, from the network clock.