Any good ideas for a wireless light meter to use with the gateway (going to ordered some esp8266 for tinkering) Say when the light gets below a certain level turn on the room lights
If where you want to measure the light is co-located with the RPi gateway, you could use the light level sensor on the BBC micro:bit or Adafruit Circuit Playground Express, and easily create a web thing using the MicroBlocks add-on (that supports the web thing library in the MicroBlocks IDE). That add-on connects to the boards over USB serial. Just plug the board into one of the RPi USB ports.
If you want the sensor remote, then ESP8266 plus any sensor similar to that of the micro:bit or CPX should also work fine, and is again easily programmed using the MicroBlocks web thing library. (Just add the Wi-Fi config block and it will expose the light sensor property as a native web thing.) If you need any help creating the scripts, just ask or check out the Mozilla IoT Activity Cards on the MicroBlocks web site.
MicroBlocks is awesome – THE most user friendly tool for creating web things that are compatible with the gateway.