high expo causes more control movement as you move sticks toward high end and this would cause over control
Expo doesn't increase the total amount of throw the surface in question has, it just moves more of the throw from the neutral point to the ends. With expo, stick movements near the neutral point give you less surface movement than if you had no expo; stick movements near the end points give you more. The total surface movement is the same with or without expo.It isn't something a tame airplane like the Kadet Senior needs, though. As for balance points, the recommended balance point on the Kadet Senior gives you a somewhat nose-heavy plane. I wouldn't recommend balancing one any farther forward than what the plans show. In any event, the OP doesn't seem to be a beginner. Beginners don't usually modify their first kits.