I love muscovies, i have 3 girls and a boy. Mine seem quite placid, they talk a lot, sort of whistling and the male lifts his mohican up and down as he talks. They have claws on their feet as they are perching ducks and they fly extremely well. they will eat mice and other small ammmals if they find them and i have read they eat baby guinea pigs so be careful if you have those. Mine are in an enclosure with chickens, chicks and geese and they all get along fine but the muscovies stick together. they are not true ducks and some believe they are more closely related to geese so i don't know if they would be happier with their own kind rather than just one with another breed, perhaps someone else can comment on that. They take 35 days to hatch and they talk to their eggs while they sit on them. I suspect the aggression depends on the induvidual, we all draw judgment by our own experience, i had a horrible maran once so drew the conclusion they were aggressive but many people have told me they're delightful!
Have you looked at feathersite its a wonderful website that shows every poultry breed known to man. good luck, Helen