Wow, that's plenty of land! As for having four hens for two Silkie roos, the number is good. The problem is with the size, but I can only speak from my own experience. I have a Silkie roo who was supposed to be a pullet, and he's a scrappy little guy who hangs with the big chicks and defers to my enormous Welsummer rooster. The problem is that the big hens don't take him seriously. I have a couple of Cream Legbars who are on the small side, and they will squat for him, but he's still too little to effectively "do the deed." One of the girl's tail feathers are a big of a mess from him.
I have some bantam pullets shipping to me in a couple of months to keep him more satisfied, and in the meantime, I'm building a separate run for him and his future harem.
