Having more than one cock bird can be problematic in terms of fighting. The question is - why have multiple cock birds? What is your end game? If you want to breed chickens, then go ahead and choose a cock bird that has the qualities you are looking for - either in terms of breed or a good...
I think that unless one is talking about mixing silkies with other breeds, then its usually fine (and many peeps keep silkies as part of a mixed flock, I should add). I think that management style and space are issues that should be considered more important. The smaller the coop / run then the...