Mixed flock advice- should I get more ducks?

[Eggstatic ChickyDoo]

Background: I have a mixed flock- 17 hens, 1 rooster, 1 cayuga drake, and 1 pekin duck. They currently have a 10x12 coop with a 10x6 covered run. In addition, they spend 3-4 days a week free-ranging from dawn to dusk. We're planning to expand the run within the next month (the plan is 10x12' covered area for now with an eventual expansion to ~20x40') and are considering adding a separate duck house, if they might use it. The duck, in particular, likes to sleep under the one part of the roosts where the poop board doesn't quite reach and I'm tired of seeing her covered in chicken poop. When she's free, she likes to sleep in an old A-frame dog house, I thought I'd build another coop with a similar set-up inside in the hopes to coax her out of her current corner.
Also, we thought we'd be okay with just the two ducks since she's bigger than he is and, for the most part, we're fine. They waddle around together constantly when they're out and although they mate pretty frequently, she shows no signs of over-mating. She will frequently stop in front of him, both in their pool and out, and wiggle for him to mount. The problem (?) is that he keeps chasing after the hens, too, presumably trying to mate them. They're all far faster than he is, they can fly just fine, and the rooster intervenes if he chases them in the coop, so no one is any worse for wear, but he does seem to long for more females, so we're more seriously thinking about expanding the flock and I'm realizing how much I don't know about ducks.
If we get straight run ducklings (which seems to be what's available locally), how long are we likely to have before we have to cull the extra drakes (eating them isn't an issue regardless, but if we can have our own duck for Thanksgiving that would be a bonus)? How much bigger should I make the new building if I'm housing a drake and 3-6 ducks instead of just the pair? Will they probably sleep together, the way the hens do, or should I have a separate nest structure for each duck? Should I even be considering getting more ducks just to increase his flock (eggs are a bonus, but we generally have enough from the hens to cover our use and a few to share; none of us has a strong preference for duck vs. chicken eggs) or is this whole idea just an invitation for trouble?

 

[21hens-incharge]

Given your current space limitations (particularly the run) I would suggest building a separate area with a ground coop for the ducks.

Your current run at 6'x10' is only truly big enough for 6 chickens. You need at least a 10x17 run for the chickens alone. Ducks need a lot more space per bird in the run in my experience.

Ducks are messy more ducks means more mess.

Drakes have an appendage that roosters do not. Female chickens are not built to be mated that way and it is often fatal when it happens.

Housing a rowdy drake with your chickens is putting a lot of stress on them.
The rooster cannot possibly protect them forever.

Recommend number of females for the drake is a minimum of six to prevent over breeding and stress on the females.

 

[Eggstatic ChickyDoo]

Thanks for the reply! This spring when things started to thaw I got a solid lesson in how much more mess there is than if it were just the chickens. I've had a few issues with MIL about the ducks, but the whole flock is at her place and the ducks are part of the deal for having chickens out there . I knew we were running a risk by having just the pair, but I had no idea he'd ever consider another species. Lesson learned!
I reworked the layout so that I could keep the 10x6 run as a separable section and run the extension along the back of the coop, then spent the weekend setting it up, so now they have 10x18 run along the back of the coop with a small door connecting it to the 10x6 and another door into the coop under the roosts. There's a 12" high ledge between the runs for now, so the chickens can access both sides, but the ducks are stuck in the old (small) run. I haven't kicked them out of the coop entirely yet, but I put up some boards to block off the part of the coop near that door, so there's a 4x10 section that everyone can get to, an 8x10 section that only the chickens can get to. I plan to frame that section in with chicken wire and an adjustable door (I forget who it was, but someone was showing the set up that they have for introducing new chicks, their divider was my inspiration). I'm hoping to use this space as a "bridge" home between when ducklings are getting big for the brooder but are still too small to run around with adults, since they'll be able to see each other from there (that makes sense, right?). Afterwards, I can keep it open but available to close off in case I need to separate anyone from either flock in the future.
So now, on to planning for a new duck house. Given the concerns about problems for Daisy in the future, it looks like Donald is going to get a few more lady friends, which raises so many questions. How big a space will I need to house 7 ducks? How much bigger for the 12 we'll likely have until we can who's who, genderwise? Should I be planning for more since 6 is the minimum recommended? Are there breeds that are quieter than Pekins (that girl screams when she sees treats!) but are still large enough to fend for themselves if they're not in the mood for Donald's advances? Do I need to keep ducklings separate from adults until they're all grown up or can I mix them once they've feathered out? How old will they be before I can tell genders apart (I don't remember when we knew for sure with Donald, but he used to be Rose until shortly before his drake feathers came in) and should I be waiting until then to add them in (so I can add just the ducks, not the drakes)? Once I have the new ducks in, do I make one big duck house or several smaller duck houses or a big duck house with partitions?

Seriously, though, thanks for the help! I've had chickens before so I thought I had an idea what I was doing, but ducks are a totally different game in some ways

 

[21hens-incharge]

I found my 7 ducks needed a 5x8 duck house. I did not keep food or water in it to keep it drier. I also had 30 square foot per bird of run space. I don't think they would have been happy with any less than that.

As you have seen the spring thaw reveals just how mucky and messy they are.

I sold mine the last week of March and am STILL trying to get that area dried out.

I certainly don't have all the answers you need but there are a lot of great duck people here so I am sure they will be along to help.