With a rag quilt there is quite a bit of fabric in the seams (at least 2 layers are stitched together, as opposed to the normal one layer in a quilt top). Because of that, most rag quilts are made with squares and rectangles, with an occasional HST thrown in. You could certainly make Ohio stars in your quilt, but you might have trouble with all the layers that you have to sew through in the intersections.
I never sew with flannel that hasn't been pre-washed, because it shrinks unevenly in each direction, and flannel is notorious for bleeding. I use flannel as all 3 layers of the rag quilt so I don't have to cut separate batting pieces, and there is more fabric to rag. I also like to mix in some corduroy for a different texture.