The ducks like the pond. The chickens do not. Thus, they stay pretty separate until I start chasing the ducks into the coop at night-time to avoid opportunistic winter predators.
Ducks are paranoid. I have ever had a friendly duck. Friendly chickens, yes. Friendly ducks, no. The females, less muscovies, are very loud. They're easy to herd. They will not want to come in at night. Your chickens might return to the coop every night to roost; ducks will try to stay outside (again, except muscovies)
Ducks can rip up a wet yard in no time flat. They'll drill little holes in the mud for food, and they'll eat all of your baby cucumbers. They glory in making mud puddles larger.
If you get ducks, it's preferable to get them sexed. You want a 1:4 male:female ratio at the very least, 1:7 is better, (That's mostly if you have more than one drake. Single drakes sometimes do alright in pairs or trios.)
Drakes and ducks operate seasonally. Spring is breeding season. Mating. Egg-laying. Brooding. Keep that in mind. All hormonal behaviours will escalate in spring. They will get louder. They will fight more. If they're a broody breed, this is when they'll go broody.
Drakes shouldn't be kept with chickens unless there are ducks as well. Drakes will sometimes try to breed hens if there are no females of their own species, and that can end pretty disastrously for the hen, as they're not built to deal with penises. I have never personally experienced this issue.