Welcome to Backyard Chickens! I think you'll find this to be a pretty friendly place, and you'll soon get to know some of the folks here that are invaluable to your upcoming duck journey!
We keep silver Appleyard ducks. They are a large breed, and we currently keep six (per zoning requirements despite the fact that we live on four acres on the edge of town).
RATIO: We have five hens and one drake. That ratio of drakes to hens is about the limit in our opinion if you plan to have them live together. Even with that ratio, we need to manage the flock during mating season, which runs from about April to September here in Maine. By manage, I mean we need to divide the flock into groups, as our one drake will often pick one or two girls to pick on (not really mating, just dominance behavior). It is essential to have a way you can separate your drake at night in a predator proof setting, where everyone is safe.
DUCKHOUSE: Four to five square feet per duck in the duckhouse is sufficient if they are only in the duckhouse at night. We have 32 square feet for our six ducks, and it works great. You can get a sense of what 32 square feet looks like for six large breed ducks in the picture below from one of our duckcams.
The duckhouse should have excellent ventilation and be draft free. We use a combination of shavings and straw, and we use the deep litter method in the duckhouse. We clean out once or twice a year. We never put food or water in the duckhouse.
RUN: Our run is covered (the best choice we ever made!) and attached to the duckhouse. It is predator proof, and the ducks have access to it 24/7 99 percent of the time. Our run is 12'x8' with an addition 4'x8' area under the duckhouse (this area can be isolated from the rest of the run) and an adjacent "annex" we can use if we need to separate birds. All said, we have about 128 square feet of run for our six ducks, and it works great. We keep a five-gallon bucket (heated in the winter) and their food/oyster shells in the run.
FREE RANGE: Our ducks free range supervised at least twice a day year-round. When it's very cold, they don't often go far, but for the rest of the year, they will range far and wide. The are also often out during the day when we are working outside. When they are not free-ranging, they are either in their run (much of the winter) or in one of two adjacent, fenced pastures. During mating season, we often have them separated into two groups, and we mix the groups up each day making sure to keep any girl that is getting picked on separate from Angus. They can all be side-by-side in the two pastures on either side of the wire fence.
GETTING THEM HOME: We have established a routine to bring them back in after free ranging, and it works great. We give them a soup that is composed of peas and greens and a mealworm crumble 2x a day after free ranging. Wherever they are on the property, we just have to call "Hey Ducklings, If you're ready, it's time for soup for ducks!" and they come running as in the video below:
WATER: We have a couple places around the property that have water for bathing and some swimming most of the year. In the winter, the water sometimes freezes for extended periods, and it may go dry in late August and into September until the fall rains come. As long as the ducks have a deep bucket with clean water where they can dunk their head, they are fine. So you don't need to worry about kiddy pools and such in the winter when everything freezes. In fact, we don't use a kiddie pool at all anymore. In their pastures when they are not free ranging, we give them small tubs like in the video below instead of a kiddie pool. The small tubs are a much better solution in our opinion because it's easy to capture and use the grey water, and the ducks seem to like them just fine. They don't
need to swim, but they sure like to

.
If you have other questions, don't hesitate to reach out. Ducks are wonderful animals, and we're excited you will be sharing your journey with us. Post pictures! We all love pictures (and videos!).