Be aware that this unofficial guide is for openHAB 1.8. @engrfash stated that he is on 2.0. The guide might still be useful to understand a few details but besides that, you should also look into the official openHAB 2 documentation. It is partly unfinished but still a good starting point: http://docs.openhab.org/overview.html
Regarding your hardware: How are you going to make your Arduinos communicate? If you didn’t buy any till now, consider buying a few ESP8266 instead (as @sasha_jpr already hinted). As for your general approach. That is of course up to you and your experience and willingness to build stuff yourself but consider buying components for the standard tasks to get to a working system faster. These do not have to be expensive, have a look at this for example: ITEAD Sonoff switches and sockets - cheap ESP8266 Wifi+MQTT hardware