those will be cute appliques! The quilt is very cute I love the colors. I have never tied quilt so I am no help there.
I have never used Sof n Comfy from Joann's, but I have used Minky backing. I never had trouble quilting with the Minky.
I have the most luck with quilting diagonal straight lines. I have an acrylic ruler that is 3-1/2" wide, so use that as my guide. I set the angle and mark with washable markers on both sides of the ruler. Then I move it down and mark the line next line and so on. then all of my lines are equally spaced (I still mess up sometimes, but with the ruler the mistakes a less noticeable)