Male ducks (drakes) will literally rape chickens to death if they don't enough female ducks around. Drakes have giant, long, corkscrew-shaped penis. Chickens are not equipped to receive an object of such...magnitude. Here's a good article on it:
https://www.nwedible.com/aggressive-duck-sex/. And here's a fun video about ducks:
Drakes are quieter than female ducks, but females really aren't that loud, unless they are really ticked off or scared. Mine only get that loud about 2-3 times a day, and also if they are separated from their fellows. I think two or three female ducks would do great with your chickens. I have a flock of ducks that vary in number between 5 and 15. Sometimes I have one chicken along with them. I find that the ducks get along well with the chicken. Sometimes the chicken would pick on the ducks, but as long as the ducks had room to get away from her, there were no problems. The ducks are also less damaging in general to the garden, and easier to keep out of beds. Just put up a two foot tall fence, or have the beds raised about two feet, and the ducks will generally avoid them as long as there are enough other places to explore. And, if they get in your garden, they'll cause a lot less devastation in a lot less time. A chicken gets in a garden and she can/will till the the whole bed up in like 30 minutes. If a duck got in there, she'd eat all your slugs and legume seeds and grain seeds and nibble a lot of your young leaves, and it'd take her three hours to do all that.
My ducks often free range over an acre for a few hours a day, but sometimes for months on end they confined to their run...which is 1,700sqft. It's taken them three years to do damage to that amount of area...and it wouldn't be a problem if I just fenced off some areas for a month so that the grass can regrow.
As for stink, as long as you change out their water daily, and do something like a deep litter method in their house, there won't be much smell at all. For water, I use oil pan-sized trays. They're about 2-3 inches deep, 1.5 feet wide and 2.5 feet long, as well as a foot tall pail for their duck house. I change the water every day. I usually put their water tray next to a fruit tree so I can water/fertilize the tree while dumping the water. After a few days by a tree, I move it to another one. This also encourages them to spread out their slug/weed/grass eating, as they like to stay by their water.
I hope that helps!