Need Guidance with my Mallard Duck raising

[freeandalive1]

I have 11 Mallards. (the 11th one was a freebie cause the store didn't want to leave it there alone). I have a 20x20 pen I keep them in for now. They graduated out of the smaller pen I had them in about 2 weeks ago. Some of them are showing beautiful colors on the wings on their side.

How many drakes would I keep after they all reveal their sex? I will gift the extra drakes to good homes.

How long before I can let them out of the pen and forage in the yard? They are mighty territorial and the 7 pullets I'm raising in a small coop inside the 20x20 can't run around in there with the ducks cause the ducks chase them. So, I have to sit out there and let the pullets get exercise by opening the top of the coop and letting them fly up to the edges and walk around on that for a while as I talk to them and pet them. If one flies down, the ducks start chasing! So I won't let the chicks out yet. There is a nice chicken house waiting in that same area once the pullets can have the pen. My hubby is putting me a new 10x20 up this week and I will transfer the ducks to their own pad. But still, how old do they need to be until I can introduce them to the awesome yard that awaits them with the 1-acre pond.
thanks