Ok. First I'd say make sure you have enough square footage to add more birds in both the coop and the run as well as add a pool. Second, ducks are different, they don't particularly like ramps or do them well and need a bigger pop hole, so make sure they can get into the coop easily. They don't roost, so they need a place to sleep on the floor as well as a place to make nests at floor level (unless you are going with Muscovy). Anyways, coop modifications for ducks is a whole different discussion. I digress.
I just want to say, have a backup plan. What if your ducks and chickens don't like each other? What if they can never live together? Can you house them separately? This needs to be done for quarantine and introductions anyway. Also consider getting sexed females. Male ducks and female chickens do not generally mix well. Having a housing plan in place before bringing them home will help much. Ducks are fun. I highly recommend them. They are as easy to take care of as chickens. You will love them, your chickens just might not love them so much.
Consider if their primary purpose is eggs, meat, or just pets.
