Should I get a rooster?
Personally I would wait. Is your plan to breed more birds?
I have 4 month old pullets right now, that I can Not put with the cockerel.
He is way to rough & inexperienced in "Amour"
The girls run in terror & scream bloody murder...it's not pleasant for them.
The 5 month cockerel ( a rooster who is not mature yet ) is now caged in another room.
I will try again in a month. But I feel bad for ALL of them.
IF you wait, you will give the girls time to mature sexually.
Plus you will have time to find the Perfect rooster.
You can usually find someone who has too many roos & wants to find homes.
A lot of times the rooster is a Pet, & can be Free or inexpensive.
Well you said they would eventually separated, so that shouldn't be too much of an issue.
If you notice the chicks getting bullied, you can divide the new coop in half.
( my ducklings never interacted with the chicks )
Ducks are Really messy & wet their surroundings.
You will notice the shavings will be soaked, & the water container will always be dirty.
Ducks will pick up Anything & bring it to the water to play / wash it.
IF the chicks are young, they can catch a chill by being in wet bedding.
Chicks need heat longer than ducks.
You might want to think about separating them sooner?
You likely won't need a rooster. I've never tried to integrate chickens with ducks, but I've heard people doing it just fine. Growing up together, they should be okay enough around each other that it shouldn't be an issue. Also, when you don't have a rooster one of the hens oftentimes steps up as the dominant chicken and will protect the flock. Unless you're having problems with them fighting, I wouldn't add one. It can be difficult to add any chicken to a pre-existing flock, let alone adding a rooster. It might actually cause more fighting!