I started with 4 ducks last year. I'm up to 6 ducks now, no males.
I used portable poultry fencing for contained foraging and free time in the yard for free foraging.
Their secure pen is dog kennel and provided about 100 square feet floor space. I had 2 dog houses in it, a 70 gallon pond with ramp, two feed pans and two water pans a grit station and an oyster shell station.
I never had good luck with actual waterers. Either I made a mess trying to fill them (bottom fill waterer) or I couldn't find perfectly level place to put them (top fill waterer) and they emptied faster than they should. My ducks didn't make a mess in them and don't usually make a mess in their water pans. I change the water pans daily and use that water on plants/trees in my yard.
They had plenty of room to do ducky stuff including hunting bugs and worms and amphibians.
I started using packed ground because we used fill dirt to fill in an area for them. I added river rocks around the water areas in anticipation of problems, put down a layer of coir and a deep layer of straw before winter. I also added in about 2 lbs of composting red wigglers. I turned straw about once a week when it wasnt frozen solid in winter. I'm in the process of switching over to corn cob pellets because theyre really soft and absorb a ridiculous amount of water.
I use either chopped super dry straw in nest boxes or shavings.. whichever is cheaper at my local
TSC. My ducks don't have a preference. They're happy to nest in either.
We're fencing in about another 180 ft fully covered circular area for them because I need to give my new practically adult ducks some space away from the grumpy broodies and a place to forage that doesnt require a person to be there.