Fun project, just the kind that I enjoy. I personally would stay with rudder control and the diehedral as designed - simplicity is nice.
However, if you do go to ailerons, I think the cambered sheet format for the wing remains fine - no need to change to a full section wing.
That servo size should be fine from a power perspective, though often the smaller servos don't do so well with vibration of glow powerplants. A 6g direction for servos might be a better option.
Have fun, and please share photos of your project along the way.
scott