We have ducks and yes we keep the two separate the ducks I change their water several times a day, and they are very messy creatures. The hen coop doesn't get that messy and the chicken poop we scoop up and compost. But ducksare messy critters.
I have 4 beautiful children, we have 12 chickens, most are Hylines, who are curious and forage all day, then we have Orpingtons, and Ancona's. We just added ducks to mix Khaki Cambell's, we have 3 sheep, 1 cat,a dog, basically a small petting zoo!
We have 10 Hyline chickens, 2 Ancona chickens and 2 Orpingtons, and have just added 4 Khaki Campbells 1 drake and 3 hens. From all the research I did that seemed to be a good number. We have also ordered hatching eggs for Cayuga ducks. They are a great duck breed