Vtol
not really sure about that part, i have pitch and yaw controlled by control vanes and bank is controlled by varying 2 engine speeds. This will be linked to a gyro to stabalise on it. Personally i would have thought varying 4 engine speeds would make it very unstable but i guess if you hook up all 3 axis to gyros it should be ok.
I think best thing would to have a control vane array but instead of using propwash and varying pressure ect. The control surfaces could be used to cover the propwsh outlets. i.e- blocking off front 2 outlets would cause decreased airflow therefore causing forward pitch. One of the hardest parts will be finding contra-rotating props and gearboxes for the engines. On mine i use the control vanes to cancel out torque reaction, my engines rotate same direction. Im counting on neutralising reaction torque by doing this.