I would not use the monofiliment. This is a baby quilt and you would not want scratchy poky monofiliment thread ends poking babies delicate skin. Additionally the older monos will not hold up to the frequest washing and drying and high temps used to launder a well used baby quilt.
I have machine quilted with the CT cotton. Aside from lint buildup in my bobbin case it worked fine. Assuming you are using a domestic sewing machine as opposed to a LA or Midarm. How confident are you with your FMQ skills? Kind of hard to make suggestions without knowing these little details. If you want to highlight the spiral then why not quilt a spiral following the spiral in your fabric? As it looks like a fairly large, gradual curve you could actually do this with your walking foot rather than FMQ. That would stabalize the quilt nicely. Once you have that done you can decide if you want to do more quilting. If this were mine I would echo the designs coming out in the tie die. Color of thread is up to you and how much you want it to blend in. Audition it by laying it over the fabric.
Edited to add... there is no reason not to use more than one thread color either.