Your quilt is just lovely! I love the easy suggestions for quilting since it sounds like you are just discovering the fun of doing FMQ! Before you know it, you will find yourself exploring more designs later. As for thread, experiment by unrolling some spools of thread on the top and see what grabs your attention and what looks good to you. This tip was passed to me by a very nice quilt store owner. Try a neutral such as a light silvery gray. Or a variegated thread with the different shades softly blending together? Light colored or medium colored variegated thread is another option. It will be fun to see what you decide to do with your log cabin quilt!