You're over thinking it. It can be more of a hutch if you want. It's mostly gonna be for protection from predators. Ducks can actually handle temps down around 0. They just need a wind break. Heat should also be kept in mind. Vents should be put in to keep it cool and clean in the summer
At that age i would give them water over night. Ducks can't sweat so they pant like dogs to cool down. As long as they're in shade they're fine. And for your pen. If its completely enclosed over top it should be fine. I always heard if a 3 year old can get into a coop then a raccoon can. Also...
Does it quack or have a low raspy noise? I would sell it for around 15$. The reason i say this is because i once purchased a saxony drake for 20 and saxony ducks are a little "fancier"
Food water and shelter. Provide that and you'll do just fine. Make sure you use duck food, make sure water is clean, and make sure they have a SAFE place to sleep at night. Good duck breed to start with. They aren't to loud, they're pertty, and they are friendly. Good luck :)
Miss Lydia I'm not sure that's true. Maggots only eat dead tissue so they could actually keep it clean. The only reason i say this is because i had a raccoon attack last year and my khaki lost her left eye. I kept her inside and it swelled and got funky. I let her out and noticed maggots a few...
I know the one time i had mallards (never doing that again) i clipped their wings. It doesn't hurt them. The reason i clipped then was because a few escaped. They don't need to migrate as long as you take care of them in cold weather.