ESP8266 circuit with an LED
Well, although your system is so tiny, you have two elements that need a large amount of energy. ESP8266 is low power micro, but WiFi have consumption peaks around 1A. I just tell you because it is something that you should take into account because depending on what you want to achieve, it is possible that WiFi is not the technology that best matches with your purpose. You are just sendind a token to turn off or on a LED, so you do not have bandwidth constraints or things like this. But related to your question, the easiest way to know how good is your approach is checking the datasheet of your step down module. Ussualy, vendors provide a charts where you can check the efficiency of the product using the Vin and Vout as input for example.