Pictures would be great! I am not sure about letting them free range with my other chickens. I'm worried about the large breed rooster trying to breed them? our rooster is a Speckled Sussex. Also not sure how they would do with larger hens. But I'll try it and if not back up plan: coop would be 6X6 run would be 15X8. Should be plenty of room for about 6.Silkies are great little birds, and if you are prepared for the broodiness I don't think there is anything much more adorable to watch than a mama silkie showing her little ones around. If you are getting silkies you may want to consider a lower/wider board for them, I know ours have liked to cuddle together in a pile on the floor or on the wide board (10") we used to have for them. We now have 14" wide sand shelves to allow birds to either lay/cuddle together on the flat sand or perch on the edge boards, I simply sift the sand clean every couple of days and the birds really have seemed to enjoy them. It doubles as a great way to combine the 'poop board' and roost together and the floor stays so much cleaner.
If you are interested in sand shelves I can post some pics of the ones we did for our coop to give you a few ideas.