Your pen sounds like it does a good job but not sure of what type of predators live in your area. We lost a drake this past December after being left out at night. Wrong time to realize you have fox in the area. On that alone, I would provide shelter for them at night. Muscovy also are originally a tropical bird; they do okay in the cold but they are not winter hearty like other types of water fowl. You should be able to tell between the ducks and the drakes now. Females stay small, with smaller legs and feet. And their voices should also be developed in the next few weeks that will give you a clue as well. Soft whispery twills are the girls and soft quite hisses are the drakes. If you have drakes, they'll breed with just about anything. You'll want to keep a 3:1 or 4:1 ratio to be on the safe side for your girls. The higher female to male ratio the better for them. They'll potentially over-breed otherwise. They'll probably breed the Khakis but more than likely the offspring will be like a mule and unable to reproduce. Hope this helps and answers your questions.