on top of what Scott said, I would use 6 boxes for 4 pairs to give them options.
You need the largest covered aviary you can afford to build.
trees, pampas grass, non poisonous plants, logs, stones, tree tops, anything you can put in there will make them more at ease and less flighty.
They are nothing like domestics, if you want them to eat out of your hand, forget it, these are for lookin at, not pets.
Lots of people dont realise that, they are a wild species and you cant get that out of them.
Ponds dont have to be massive for these as the are not divers, but again bigger is prefered and will cut down on so much cleaning.
Nest boxes for these on average need to be 18" tall x 12" wide, about 3/4 of the way up on the face cut an oval hole 4" wide 3" tall, this is perfect for both species. 1/4" hardware cloth on the inside face of the box is nice to aid them and any ducklings in getting out (though I always preferred to hatch my own)
These two species are genetically impossible to cross, so you are good there.
They love to perch, so anything arial you can put in there is a plus, especially around the nest boxes.
As treats, they and all wild species LOVE floating catfish feed. Other than that, any commercial maintenance and layer feed is fine, dont have to be anything special, mine always got Purina Gamebird Layer, and some corn in the winter for a little extra fat layer.
Aside from that, that's about it, let me know if you have any specific questions