So I did get the muslin cut out and put together last night. I cut a size 12 (based on the body measurements given on the envelope) with no changes before cutting it out. I think I'll go down to a 10 and add some length for the real thing. I don't like struggling to get my jacket on over my clothes, but the fabric I'm going to use is a stretch twill, so it will have some give.
From the side you can see that there is a bit of a wrinkle/caving at the shoulder on the sleeve. I think making it smaller will help that. I'm wondering about the sleeves. They are supposed to be cropped and I like the shape, but I don't know if I will like that for outerwear. I'm going to let that simmer for the rest of the day.