Goat-Walker gave you great answers.
The only thing I would have added about their flying is; I clip the flight feathers on one wing to prevent it because I have found (the remains) of a couple hens in the dog yard. NOT a fun thing to come across.
My 2 Drakes are too heavy to get more...
Beautiful ducks Bleenie
I like how your pools are in a 'fenced' off area with straw down. Do you find the water stays cleaner longer using that method??? I think I will be doing something like that if you report a positive outcome.