That is a beautiful quilt. I am assuming that you are doing machine quilting since you said SITD. If I were handquilting it I would simply use masking or painter's tape in the widith I wanted to make the lines. If you are doing squares it is easy just start anywhere stitch along both edges of the tape and then move it. If you are doing it in diamonds or on the diagonal you have to make sure your first piece of tape is on the angle you want and go from there. It makes a lovely background for your type of quilt. I have done it dozens of times. If you don't want to cross through the appliques just stop and restart on the other side. That techique really will make your appliques pop!