There is a collection of techniques that can reduce energy consumption of the Nano. (eg, remove power applied LED) I've read about µA's during sleep periods. The ESP-12F clearly achieves this and can be a MySensors by adding a radio. Note that if WiFi is not disabled, savings are probably lost because the WiFi is energy hungry. This would have me leaning towards MySensors rather than ESPHome. My experience tells me that the Nano is more durable than the ESP. Another tip: If you're going to put your sensor in a harsh environment, after you have assembled it, "paint" it with electrical lacquer.