On my first string quilt, I had the same question. I just made one string block (I used a 10" square base) with the 2 1/2" strips and found I didn't like it. Made another out of strings of various widths and liked it much better. So I suggest just sew one block and see how you feel about it. And if you decide to cut your 2 1/2 strips up, I didn't measure the widths, just folded and cut. sometimes 2 strips, sometimes 3. I really like the narrower strings best.