The potential for ducks to be nasty is just like chickens, some breeds are more friendly others not, raised right most are just fine. Drakes(male ducks) you gotta watch, i have kids but mine aren't little there all teens. so are well versed in proper handling.
Ducks are messy, they as Amiga said are waterfowl, they adore mud, MUST have water to eat and dip their beaks into(cleaning the nares) and an occasional bath is important, you know how chickens dig? well ducks make mud and drill holes lol
They don't go to roost up(or flop like our silkies) like chickens, ducks vary in their desire to be in housing mine have all been taught too that doesn't mean it always goes as planned, i get the odd decenter but usually resolve it as i teach all ducks to herd, but they are not in the coops like chickens, i have managed to get mine trained to return to the penned area surrounding their barn at dusk but after that i herd into the coop and barn.
A drake and a rooster, hard to say? our roos are nowhere near my drakes.. i mainly keep scovies they would clean the clock of a silkie roo.. roos are bold though, so are drakes hard to say, definitely male hormones get going so would require close watching.
I am more duck than chicken here.. the chickens are closing in lol but i focus mainly on the ducks, so my set up is all about them... only my standard chickens free range(all hens) they hold their own with the scovies though, my drakes have never once touched a chicken BUT the risk of a drake trying to mate a chicken is a real possibility an another thing to watch for.