We always recommend finishing the facilities before introducing the birds. How large and how fancy is going to depend on space, budget and personal taste. Many features in a waterfowl set-up will be common to all species and breeds; security, water provision and access.
We would hope that starting to keep waterfowl will be the beginning of a long-term adventure. With that in mind, it is worthwhile considering how you will manage when you are not so fleet-of-foot. Small things like designing in access for a wheelbarrow or buggy for delivering the feed make sense. Next year, assuming you keep males and females together, you will hopefully have more birds than you started with. What will you do with those youngsters?
Many of us find our facilities growing in an organic way. We learn from our first steps and tend to expand. Planning the order of work is not necessarily a skill that we all have, so it is worth visiting other keepers to learn about potential pitfalls. For instance, if you get a digger in to create a pond, might you prevent access for using a tractor-mounted post knocker?
Even if it is just on the back of an envelope, it’s worth making a plan!