Ours are for pest control and eggs. Mine are a dual purpose(Muscovy) so you could use them as meat if you wish(we do not) Our ducks being a larger breed is less prone to air predators and are excellent foragers.
Ducks are messier than chickens though, water is the main cause of this they have to have it, and it must be deep enough to clean the nares. A kiddy pool however is fine for bathing/cleaning.
An unusual trait of my breed is the do in fact roost like chickens they are also(mainly the ducks) excellent fliers. Breed wise depends on what you want, some are better meat birds, some are better layers, better brooders, better foragers and so forth.
Housing wise, same basic idea as chickens somewhere to keep them safe from predators and the bad weather.
