I saw a website where they were doing this, but I cannot find the link just now.
Anyway, with numbers like that you'll run into what they did on their farm, where all the vegetation soon is gone and only dirt and mud remain.... unless you rotate them as well as
Joel Salatin does his cows.
Having said that I will add that ducks do not require housing. They do require predictor protection and housing is not the best way to do this, and here are my reasons; ducks are much messier than
chickens, their poo is runny/stinky/dirty and they do not scratch so they really don't cover it even by accident. Bunching up a good amount of ducks creates a nasty place fast where as with free ranging there is no nasty. I have found this one factor (stink/mess when confined) to be the biggest reason people prefer
chickens over ducks. This is not me, I prefer ducks myself, and have helped many to get started with them, but when done wrong they all back out in a season or two.
What am I saying.... think about duck keeping different than any other animal, you want to keep them moving, foraging, poo and go. They prefer to create nests inside bushy plants, and if you always leave one egg (the newest) they will continue to use that nest. Take all the eggs and they will move. If you would set up
enough paddocks, that where large enough, with some kind of bush in one section preferably the middle of the paddock, and grasses, leaves and old rotten logs (short material) everywhere else. This could work. The ducks will use the brush for their eggs, and forage the rest. Being on the move would keep their droppings from overwhelming the soil and plant life, and proper fencing will keep their predators out. It is not perfect, and I feel this is why many don't keep ducks.
The website I was looking for uses electric netting only a couple of feet high and they move their large flock. Also, I do not remember the breed they were using, something heavy, but some breeds are prone to flying like Mallards and will fly away easily if spooked by you or predators.
Ducks are also more like cats, they take cat naps during the 24 hours cycle. They are more quite at night, but that is really to keep a low profile with the night predator population. They don't 'sleep' as we know it at night, they don't roost (unless raised by a
chicken) they just quite down, move much less, sit and watch, then move then sit again. They do forage, but mostly during dusk and dawn and daylight hours. So you see locking them up at night is not very humane as they still want to move. And should it rain they want to be out in it, this is one of their joys in life.
The good news is this instinct to be on the move makes them great foragers, pest control/patrol and clean - if you don't close them up in a barn or house.