Generally speaking 4 sq. ft. per chicken plus 10 sq. ft per chicken in the run.
So 6 chickens. But they are bantams. You can fit more.
If you have cold winters they will live inside and don't crowd them. So if cold winters I would go with 4. If they will only sleep in there at night and you have mild weather I would go with 12. But they go broody so much that you need a LOT of nestboxes.
I mean a LOT of nestboxes. So I wouldn't really recommend 12 chickens in there! Chickens need generally 5 chickens per nestbox but when they are broody they live in the box and then other chickens can't use it.
I love silkies. They don't like ramps, BTW. But you can train them on the ramp. Keep food in coop and don't help them down ramp. They don't fly.
Oh wait just reread your post...you already have them so you know what they are like.