Ducks are much messier than chickens, especially as littles. Because of that, I'd consider not brooding the ducks and chicks together. Ducks make a mess with their water and bedding will get wet unless you stay on top of it. While my chicken as an adult doesn't care, chicks can get chilled if the water mess isn't managed well. Amiga gave you links that can help, but be prepared that you might still need to separate them just due to water.
That and rounded bills vs pointy beaks... sometimes don't mix well in the brooder. And it isn't always the chicks that pick on the ducks. Also, ducks are going to grow faster than the chicks and that could lead to some issues. Just be aware things can arise and if you do brood them together, at some point, you might need to move to plan B.
As adults, my chicken has a house to herself and the ducks have a separate house. I hose the duck house out daily. The chicken didn't even poop in her house at all for about 2 weeks.
Ducks make a muddy mess of their water. My chicken doesn't care. She has her own clean water they can't get to, but she doesn't touch that and just uses the messy duck water.
My ducks have a bin of pine straw which is where they normally lay their eggs when they are laying. Sometimes they will lay them in the yard, pond, or willy nilly in their house not in the box, but usually in the box. Ducks don't need roosts (muscovies will roost, but the mallard derived ones will not)
I use a flock raiser crumble to feed littles. Then once old enough, they all go to chicken layer feed.
Breeds - depends on what you are looking for in a duck. I have had runners, welsh harlequin, a buff and a mallard. The buff and mallard were not long lived due to a fox :( but the buff as was a male and a sweet little guy that loved hanging out with his mallard girl. The mallard would fly and that's how she became a fox snack... she flew out of the pen, probably to their pond and was likely taken as a result. But she was a loud mouth. Very sweet girl and very bonded to the buff and you could tell she was not happy when the fox got him. My runners are quietly talkative girls. They love their pond and just seem to have fun. My welsh harlequin is a hoot to watch in comparison to the runners. So very different in movement, but she keeps up with them. She is typically quiet unless she has something she thinks you should know about and then she tells you loud and clear!
All my girls were louder in their first year and then quieted down. They chatter, but they aren't too quacky too often.
Boy ducks - they can injure or even kill a chicken if they try to mate with them. Boy ducks are anatomically different than roosters. I didn't see my male trying to mate the chickens, but he had plenty of ducks to keep him busy when he so desired. With just 2 ducks, I'd not get a male since you also have chickens.