As long as your looking for a domestic breed I have information. Ornamentals are a totally diffrent story!
What breed are you getting? The size of the breed will slightly change how large a space they need.
For a medium sized duck their coop should be about 3 square feet for the first duck and 1 additional square foot for every duck after that. So for three ducks thats a coop with a floor space of about 5 square feet.
As for an outdoor run something with about 15 square feet of floor space or larger should do.
This is about right for medium sized duck breeds (e.g. Pekins, Runners, Rouens, ect...)
For larger breeds like Muscovies you will need more space while for bantam breeds like Calls you wont need nearly as much space.
They will need:
A main feed (I recomend Mazuri Waterfowl Maintenence) They can be free fed this. No medicated feeds!
Grit (we use fine granite grit used for chickens. Usually Mana Pro Grit.) this can be sprinkeled on their greens every other day!
Greens (Romaine lettuce, Dandelion greens, NOT spinnach!) They will need these daily. Especially in the winter or when they cant be out on grass.
Oyster Shell (feed this in a seperate dish so that they only eat it as needed) oystershelll supplies calcium which the girls will need as they start to lay.
And treats! (e.g. Tomato, peas, banana, the ocasional meal worm, cricket or feeder fish, hard boiled eggs, My duckies love preety much all veggies except carrots)
As for what not to feed them:
Avacado, Spinach, store bought night crawlers, grains, seeds, nuts etc...
They can be housed with chickens as long as they are fed seperatly. I'm not sure about turkeys but I assume as long as they eat seperate feed they should be fine.
Good Luck
Emily