I would use a middle layer of flannel rather than batting. You wouldn't have to worry about it bunching up. It seems like it would make a cozier quilt with the flannel middle layer and won't add a lot of weight. When making rag quilts, I sew an x through the blocks to help stabilized them. You can choose whatever size blocks that work for your fabric or design. Keep in mind that you will be cutting around each block, so it seems the smaller the block, the more the cutting.