Okay, first off, if your coop and run isn't completely covered, they will free range themselves.
I have never found them to be aggressive. Well, except the males towards other sumatra males.
I am currently in the market for a male, but I know people that have them in a mixed flock-I would suggest that if you get a male, that he be the only male.
Be careful; I have found that they outshine all of my other birds(I think that they are gorgeous!), and make me think unkind thoughts about my poor dumpy JG's.
I actually loaned one of my hens as a showmanship bird for a 4-Her in her first year of poultry-she did great! ANd since that hen went to state fair and got Best Of Show Large Fowl, she's been a total diva.
One thing: caging them is so not a good idea. My poor girl beat herself against the cage and broke many feathers; if she hadn't, she would have taken best overall bird.
I've also noticed that they tend to hang with each other, and not truly mix with the group, and they don't really seem to have a part in the pecking order. They just sort of do what they want.