Most of my time designing hardware is spent trying to find ways to prevent the doofus writing the firmware from releasing the magic smoke. I am that doofus
Addressing some of the comments/concerns in your documentation:
* To protect the ultrasonic mister from bad firmware frying it, you could probably replace R6 with a sufficiently sized capacitor to make an effective DC block
* I've also had issues with a thermal sensor just reading board temp, best solution is to make the sensor a separate board. Short of that, one can mill slots around it and reduce copper pour to reduce thermal conductivety from the PCB.