Dihedral: don't know the theory, but current designs have the top surface more or less flat, with the dihedral provided by the difference in thickness between root and tip.
Again,in practice, very few designs get this spot-on---the test being how much rudder-to-aileron mix is needed for no roll when rudder is applied.
As a general rule ,the more "low wing" the design, the more dihedral will be required, and the nearer it is to mid wing,the less.