Re: Control electronics
Actually, the height difference between the wingtips would be an excellent approximation of the actual bank of the craft. There would be a small displacement due to the flexure of the wings, but (a) this disappears in differential measurement and (b) by symmetry the angle of bank at the fuselage is parallel to the angle between the wingtip sensors — certainly within the tolerance of the sensors. Furthermore, by separating the accelerometers by a metre or whatever, they should be able to achieve greater precision than a solid-state gyro in a compact enclosure.
As far as variations in GPS altitude, we should be able to refine the reading by averaging out all the values over the past few seconds. We will know (from the IMU) when we are in a steady gradual drop vs. a sudden gut-wrenching air pocket. Therefore we can use the data stream, integrating it with weighting more recent values more strongly, to get a pretty decent absolute altitude measurement. That can be used to update the IMU periodically.