Stab size is important in terms of pitch stability. Depends entirely on the kind of flying one needs the model to do. For older pattern where a model essentially drew straight lines and curves with large radii, a larger stab produced smoother, more graceful flying. That is, larger stab as a percentage of wing area.

Present day patterns require much greater acrobatic ability from a design, with ability in both smooth lines as well as snaps and spins, in various attitudes. Smaller stabs will reduce the pitch stability of a model and allow it to perform far more aerobatically than the earlier designs could.

Stab thickness matters little as long as it is within reasonable window. Too thin and structure becomes unstable. Too thick for the chord involved, and desired crisp response maybe compromised.

Tail Volume Coefficient is a parameter that should be understood by anyone designing. In my experiments, TVC's within a certain window produce snappier, crisper maneuverability, yet straight lines and smooth curves are easily flown as well.

Fin/rudder size affects yaw stability just as a stab affects pitch. However, unlike the horizontal surfaces (stab vs wing), the vertical stab only has the fuse to stabilze plus the vertical component of the wing area(due to dihedral.) Older designs tended to have wings placed lower in the fuse which meant more dihedral and hence a greater vertical area component. We could get away with a pencil thin fuse and still have decent yaw effect because of the wing dihedral.

As wings were raised, they had to get flatter for reduced roll coupling. That tended to reduce rudder effectiveness, since the effective fuse lateral area was reduced. These models were extremely stable in yaw and had trouble performing crisp snaps and spins. Fuses required a deeper section around the cg to get improved rudder effectiveness again. That's where we are today.

It isn't that compex but I have oversimplified it.

MattK