Yes big space is always the key.But as the birds are growing up your going to have to raise a them side by side and in someway interact with all of them,atleast make them comfortable around one and another.There are certain waterfowl who actually don’t spend their entire time just playing in water,such as geese.Surpisngly they don’t really spend as much time as ducks do in water,unless their only flock is ducks.
You will still need separate cages.But the thought of free ranging them all in your property is ok,how many acres do you have?