wta12, to calculate your condenser you need just basic knowledge.
Q=k x F x dT
Q is capacity, F is surface of your condenser, dT is temperature difference between refrigerant and cooling water. Usually in water cooled condenser dT is 5 K. In your case dT should be 15...20 K. So your surface should be 3...4 times smaller. But pay attention to pressure drop if you apply small condenser.
good luck