The first post says the PIR isn't working if that's it , is there any sign of life in it at all?
Did you put an LED in there to confirm power up?
The LM2596 is supposed to be good for 3 amps however it needs 4.5V minimum input . Does it have that. I assume its the variable output type not a fixed output . I just happen to have received 10 of them today and am testing them . They don't like a lesser input voltage from what I have seen so far.
The post before gives a site on which the same problem is discussed and I saw two useful things to try
1/Ok I covered the back of the PIR circuit with aluminum foil and it works great! No more false triggers from ESP8266 noise.
2/Probably power supply - the esp8266 can draw large pulses of current when transmitting. This probably gets coupled into the pir circuitry. Use a diode and electro to decouple the power for the pir.