Does the size of control surfaces affect maneuverability, and if they are smaller, is it easier to stall?
There are at least 3 possible cases and unfortunately your question doesn't tell which one you would consider valid.

The maneuverability (the maximum rate of rotation?) can be measured by the moment of the force exerted by the surface at the CG.

Let's consider the area of the control surface is smaller, and...


All other parameters are unchanged, in particular surface airfoil, center of pressure, and angle of attack:



As the currently selected answer tells, the maximum lift available from the control surface is lower, hence the maximum moment is lower, and the maneuverability is reduced.

As the airfoil and the angle of attack are unchanged, the stall characteristics are unaffected.

This theoretical case is unlikely to be seen as the designer would certainly compensate the reduction of the area by some other change.



The surface is moved to a location further from the CG to maintain the moment with the smaller lift force:


Neither maneuverability nor stall characteristics are affected.



The angle of attack is increased to generate more lift and compensate for the smaller area:


Maneuverability is decreased as the maximum lift obtained with the maximum angle of attack is decreased.
Stall is easier to trigger as the angle of attack (for an equal moment) is closer to the stall angle.