Sounds like you've got a good plan but if I were you I'd go a little taller on the height of the pen to save on your head injuries!
Also, we've got a lot of land but where my ducks are is not that big of an area at all. I have 2 runs which communicate with each other but can be closed off too. I used 2 100' rolls of fencing. I used 100' of that fencing for my inside run which would be plenty for you with just 3-4 ducks and you'll be surprised how quickly you will be fenced in. Attach it to or around the pen so you just open the door in the morning to let them out into their run, put out the food and that is all until night time. 100' may sound like a lot but it really isn't once you start running it. I have a chair I keep in the run so I can sit and be entertained.
My larger pen, where I have 7 ducks, is the size of a full sheet of plywood 8' x 4'? I'm not sure of the width measurement but they have plenty of room and almost always lay their eggs in there. I thought about putting some ducks in the other pen but they all want to go together so they do. If you look back to the picture I sent you yesterday on the left side of the pen I laid some cardboard up against that side because of the cold but it's all open with hardware cloth on that whole side except for about 1/2 way up in the back. They have tons of ventilation which is important.
I'd wait until warmer weather to get the ducklings so you won't have to worry with keeping them warm. That's what Miss Lydia is doing. Her's come in April. You won't believe how fast they grow! I agree that if you have no more room for more ducks it doesn't make any sense to get an incubator and hatch yourself although it is most excellent to watch the whole process! My neighbor lent me hers last spring and I enjoyed every bit of it even though I was clueless and a little bit scared. I watched so many youtube videos and did so much reading and then I joined BYC so you're already way ahead of me!
