It is so easy to over think color groups, designers and so on. I don't know a quilter that hasn't gone through this more than once. I love your fabrics and they will work perfect no matter how you place them. Me, I would just let the pieces fall where they may and I have no doubt this will be a perfect quilt. The flannel should be used for something else and use all the cottons for the quilt at least that is my thought.