Hi Phill,
I am glad to see you post your project here as I do not visit Facebook. Your approach looks good and is very pragmatic. One thing to consider is that before testing transitions to forward flight, you first test the BARO and GPS sensors; QSTABILIZE, QHOVER, and QLOITER. In this manner, your emergency fall-back mode becomes QHOVER or QLOITER (instead of MANUAL) in case you have a failure in forward flight.
So on a normal APM Plane setup, we use MANUAL as our emergency fall-back mode. On VTOLs, we use one of the Q modes. I don’t even have the MANUAL mode as an option on my VTOLs.
Good luck! I am looking forward to your progress…