you should wait about 10-20min to first time to setup all... after that try http://local_ip_addres_here:8123 and it should be working..
than you need to add mysensors as component, look here: https://www.home-assistant.io/components/mysensors/

Hello,
I'm using hassbian, and to edit .json, prior to that, I just stop homassistant , edit file, save file and start homeassistant service again... all working..