We keep Kahki Campbells and they are good egg layers. I think I read that they will lay 300 eggs a year though we do not keep records of ours. The eggs are slightly bigger than Hen eggs and lovely for cooking or baking. Ducks need a simple shelter that is fox proof, if you are bothered by foxes, and dry. They also do need water, preferably to swim in but they need to be able to submerge their heads in water or they may get eye problems. If you want to see any of the eggs, don't let them out until about 10am when they should have laid, otherwise they will lay anywhere!
Good luck
Dave