Welcome to the world of duckdom!
There's a LOT you need to learn before taking the plunge. Ducks require a lot more time and energy than chickens do, but in my opinion they're ten times more rewarding! Is your yard securely fenced off? If not, a doghouse just won't provide enough protection from predators. If you have sub-freezing temperatures in winter you're going to want a better insulated nesting area where they can stay warm and out of the elements. as well.
As for gender, if you're only getting two I recommend two females, although a male/female pair is good if you plan to hatch babies. Just keep in mind that with only one female, you may have to separate them at times because he could overbreed her. Two drakes will get along great too, but you won't have eggs and if a female ever comes between them it'll be a disaster, we're talking armagedduck!
Then there's the issue of food, foraging, noise level, and the fact that ducks are very, very good at getting into trouble. But it's all part of their charm.
Sorry to throw so much at you at once, I just get so excited when someone says they want to get ducks! Best of luck with your new feathered babies!
