Yes, absolutely do not make the quilt first. Make lots of extra squares to write on. Even people trying to do the right thing will mess up occasionally. Iron the squares onto freezer paper to give stability. The paper frame is a good idea, if it can be properly placed around the square, but I'm not sure how that's done. I would leave more than the desired 1/4" so you can trim the squares later to get rid of any fraying and to best frame the signatures. Do some laundry tests first with the pens and fabrics you want to use. And have someone nearby while the signing is being done to give instructions. I think a signature quilt is a wonderful idea and it can become a family heirloom. Best of luck and be sure to post it when it's done!