I would definatly say Roo now looking at that pic. Check out my aviatar, notice the round puff ball on her head. Yours has streamers. But I would still wait for that crow to be sure.
I personally use medicated feed for my chickens which are also egg layers. As far as treats there is a great chart in the learning center that has a bunch of "human" food that chickens love. Just search treat chart.
My guess would be a pullet. I am basing this off of the comb and the head shot in the second picture. It looks like a perfect little poof on top. I didn't see any streamers. But that's just my guess, I'm still new at raising silkies.
I have two silkies and a bunch of other LF chickens(30 some) and they all stay together in a big coop and run. I think it's going to be a personal decision on your part, if not a decision on weather your other chickens except the new silkes. Good luck and have fun with your new silkie chicks...