They shouldn't get old to lay eggs and mate. They should be processed (or sold in your case) before 6 months old. 3-4 months is the best time to process red rangers.
10 x 10 for the chickens
8 x 6 for the ducks
Will the chick pen be merged with the chicken pen, or will they be separate forever? Either way, you will need it to be 10 x 10.