Can you get an expert to fly the first flight? If so, I'd just set the throws about 30 degrees, then ask the expert what he thinks. Most trainers need very little aileron throw (like 3/8" each way), and having too little is not too big a problem on the first flight. Trainers don't need much elevator either (1/2" each way is usually enough), but it can be hard to land the plane if there's not enough. The rudder is not important, as long as you can steer the plane on the runway. Forget about high/low rates on a trainer. If you're really nervous about it, most of the Great Planes manuals are on line, so you can find a similar plane, and see what they recommend. A trainer is pretty much a trainer.