Wow, what a treasure! I love that she stuck to a limited color palette with this. I can't answer your question about hand-quilting a king size quilt, but I think wool is definitely the easiest batting to hand quilt through.
I've tried to big stitch quilt some sample blocks with both Warm and Natural and Quilter's Dream Select cotton and of the two, the QD was definitely easier because it doesn't have a scrim, but still not as easy as the wool. The needle glides through the wool like butter!
Now having said that, I do think that you would get the most "authentic" 30's look with a cotton batting.
And I would agree with you about echoing the hexes.