Nice howto! Just wanted to mention, the humidity sensor MAY show a significant offset when exposed to high humidity for long periods of time. It's a feature of almost all capacitive humidity sensors and especially these cheap ones. I have expensive Sensirion sensors (DHT22 is a clone I believe) and even they have at least +/- 5%RH accuracy in high humidity + the offset of 3%RH or so after some time in high humidity. Of course in a terrarium +/- 5%RH is enough. You could have another system to check the sensor in the terrarium for offset every now and then.
I myself have not use