I can not answer the other questions with any degree of authority but: as to having the leading edge of the aileron slightly thicker than the trailing edge of the wing where the aileron attaches has often been shown to be beneficial in minimizing the onset of flutter, maybe by increasing stiffness as well as helping reestablishing airflow. Another thing often not considered is where the aileron horn is attached. It should always be at an add division of the span of the aileron, i.e. 1/3, 2/3, 2/5, 3/5 etc. as this minimizes the chance of inducing flutter due to the harmonics caused by span wise flexing of the aileron. You still need to shoot for the impossible, as stiff as can be without adding mass. While a counterbalance is usually beneficial, it has little or nothing to do with reducing flutter except for the fact that adding it probably changed the mass (and subsequent resonant frequency).Mass balance does minimize the forces required on the servo though, especially under high G loads as the effects of momentum balance out relieving the servo of having to overcome that force.