Depends on the duck. You will also need to get more than one duck because they will get lonely. My pekins would go in their house at night when I told them it was time for bed but never on their own. I used treats to get them to associate their house as a good thing.
My two Pekin ducks live with my Dominique hens, and they get along great. They are all the same age (less than two weeks apart), so they were both little chickies when we started, but the ducks grow so fast they're like Baby Hughie compared to the chickens. So, with that, the ducks were much larger than the chickens in no time.
Originally I started with four chickens and one duck. The duck initially imprinted on us but then transitioned to the chickens. Next thing we knew the duck was out foraging with the chickens and was 100% part of the flock. In fact they watch out for each other. I have seen chickens run up and peck the back end of cats and seen the ducks let out warnings when they spot a hawk or other predator.
I wanted another duck (a drake to breed with) and since ducks can be amazingly loving and sociable animals, so I wound up getting another. This one was already grown when we got it and apparently not had a lot of, if any, human contact. He is a butthead, and is slowly teaching our duck to be standoffish and un-trusting, but he also lives in the hen house.
As for the accommodations, I haven't had any issue with the chickens pooping on the ducks, nor have I had any fussing over nesting boxes or anything else - they share it all and are great together. My hen house is an old 10' x 6' dog run that has a cement floor and hardy plank on the sides. Across the short side, approximately two foot from the wall, I have two roosts (at different levels) for the chickens, and a step up area (wood) underneath, which is where the ducks stay. I put an old dog cage with hay in there but they prefer staying in the corner. To keep it clean I have about 3"-4" of sand and once a week scoop it with a kitty litter scooper.
Before we started using this hen house I had one that I had bought. It was big enough for four chickens but the duck was too much. She would get in between the two roosts and take up half the hen house, and try as I may I could not get her to go into the hen house willingly. Initially I tried treats and snacks, then that turned to me chasing her around and around the hen house every night. Closing the girls up became a chore I dreaded. Putting them into the bigger hen house they all put themselves to bed now, so all I have to do is close them up. During the winter I have to wait til rather late though, as the ducks burn the midnight oil, sometimes staying out in the yard til it's completely dark. They can see much better than the chickens when it's dark, so they push the limits as far as when to go in for bed.
Anyway, my point is - regarding your question..... Your duck would get the point quickly, whether or not it cooperates is a whole other story. My duck will now go into the original hen house, but she utterly refused when that's where she was supposed to bed down. With more room and better accomodations in the bigger hen house she puts herself to bed without an issue. If you're raising her with chickens I would not bed them down separately. In our group, the ducks and chickens are one flock, and trying to separate them results in my duck carrying on like she's being murdered. I penned her in the yard once and by the end of the day she had literally worn a path thru the grass (down to the dirt) along the fence line. She paced all day long squawking for the flock.
As for the duck being lonely - Everyone said I made a big mistake only getting one duck, and when I went back to the hardware store they were sold out, so I was stuck. She flocked up with the chickens and was absolutely fine. I did wind up with another duck who quickly became her buddy, but I think she would have been fine alone. If you're adding a duck to more grown chickens or an existing flock I would say you should definitely get two, but if they're young chickens I think one would be fine. And of course, if she's lonely you can diaper her and bring her in the house!!
Check into ducks entering chicken flocks that have a rooster if you have or plan on getting a roo. That may be ugly, I'm not sure.
Good luck! Hope you get a Pekin. I love mine!