So excited.

I just went out to close up the coop for the night and encourage the ducks to go in the duck hut. And to my surprise the ducks were already snuggled into the hut. I was so proud of them that they went to bed without me having to make them. I think about not closing the door, but I'm always worried.
Do those of you that have ducks lock them up at night. This is my first time with ducks as an adult. I had them growing up when I was really young. At that time the only thing that I did was pour their food over the fence once a day when my dad let me. I'm kinda learning on the go. I have the big wall of the hut insulated. The one that is tin is the big wall. I wanted to make sure that it stayed somewhat warm. I have also added a nice bed of straw thanks to the farmer down the road. I traded a dozen eggs for some straw. Will that be enough for winter? I don't want them to freeze. I figured that if there was a night that was super cold I could put them in the coop with the girls. The coop is well insulated. What else do you all do to get ready for winter. I am going to get the coop scrubbed clean next time I clean it out, but it isn't that bad since it is new this spring. This will be my first winter with chickens and ducks and I'm worried. I have a feeling that it is going to be a bad winter and I want to make sure that I'm as ready as possible if it is going to be bad. So any advice on what else I should be doing or should have ready.