I have made 6 rag quilts so far and I have opened my seams but I don't think that it really matters as you are going to be cutting them. but it is less bulk going thru the machine if you open them. As for washing your flannel that is up to you. Rag quilts are very forgiving and if your seams don't totally line up it will be okay. When you wash the rag for the first time just make sure to keep checking your lint filter in your dryer it will fill up fast. I empty my out at least every 10 minutes. If you have any more questions don't hesitate to ask and please post a pic of your finished quilt. We'd all love to see it. Good Luck.