Nice setup! I fly a stock DJI 450 with the APM2, recently upgraded to the Ublox GPS (what an improvement!!). It took me more than a week but I think I've more or less ironed out the settings to get me a very stable flight especially on automode.
I've been contemplating on building a microquad (that runs off the APM2 board, I'm hoping to keep it at 20cm width max.. not sure if it'll be possible...
Okay happy flying, don't see many multicopters out in the field.. :(