Bree has given you some great advice. If you are a beginning quilter, keep your quilting simple so you don't become frustrated with the process. You mentioned having had to rip out and this is one place you don't really want to do that, especially with machine stitches! I like the suggestion of gray thread as it should work in well. I, too, have used monofilament on the top and have had good luck with that, even with wear and laundry. If you decide you need more stability inside the big squares, you might consider just a simple X or could maybe put a few ties there. Stitching around the designs will be tedious and might become more than you really want to try on a domestic machine. If you decide to outline though, consider some hand quilting to see if you like doing that. Yes, you can utilize several methods on the same quilt.