Not for a rudder for the light wind conditions you stated above, as it has low cLmax. It is optimised for laminar flow at low cL and maybe cavitation resistance.
The effect of lift and cavitation is very noticeable, as the boards have to provide all of the lateral resistance. On the other side the profile drag of board and rudder are only a minor part of the total drag build-up. Saving 10% of a little bit isn't worth to loose 10..20% of all your lateral force.
It is probably better to maximise the section for lift and reduce the total board area, if you dare to.
Considering the aspect ratio or better span, you should consider the maximum depth you want to have. Long boards prevent the boom from swinging free when they are up and you have to manouvre at the beach, confined water, etc. From a pure performance point you want long narrow boards, but this is limited to the minimum chord and the ever increasing bending moment (longer board, which is thiner because of low chord,if you kee the area constant) which finally leads to breakage. Selecting a thicker section with slightly higher drag helps to go for higher span as it is more resistant to the bending moment. I think a NACA 0012 is overall better than the Eppler section for a cat. It could be modified with a more forward maximum thickness position and a pointier nose for your light wind specification.

Cheers,

Klaus