Keep at it! I'm working on a similar project, using the Megatech Nirvana II as the basic platform.
So far, I've got the BNO055 IMU steering and GPS waypoint navigation working perfectly on a simple twin screw electrically powered model, and can set any powered course I like.
Next step is to come up with wind speed and direction indicators, so I've downloaded your Github material and will take a look at what you did.
Thanks for posting!