The stock KK does not build heavy so doing this type of cutouts on the foam is not need but can be done if you want to save a few ounces. Go easy on the glue when skinning the wing and you will have a fairly light wing. The plane is relatively small so a standard .60 will fly it nicely. I powered mine with an OS .61 FSR. If doing one again I would add the servos in the wing and as I said before make the plane a tail dragger.