You do not have to do STID. In fact, I rarely use that at all because, if seams have been pressed open, what are you stitching on? I often use an echo stitch and I have a favorite presser foot that has very good markings for the width and for where to pivot (I like a slight bit less than 1/4"). If you are doing every HST and Square, you will have a lot of quilting. You may want to think about which ones to do to keep within your 5" or 6" requirement and have a nice pattern on the back without doing every single one.