Yes, you can eat duck eggs. They are richer with a larger yolk and thicker white but taste similar to chicken eggs. They are available overseas in grocery stores. They are supposed to be great for baking. If you have males just collect your eggs and refrigerate in case they are fertile. Putting them in the fridge will not allow any development.
As for how often, some ducks lay 1 or 2 eggs twice a day.
A Drake could be hard on the hens. He will attempt to mate anyways and would not be gentle about it. If you wouldn't want ducks around for him to release his tension, I would go with a duck over a drake.