For thread selection, if you use a very light-weight thread, it will sink into the quilt and you'll see mostly the quilting pattern, not so much the stitches. I have used Connecting Thread's "EssentialPro", a 70/3 weight (no affiliation, just a fan). I really like this effect.
Most cotton thread is 50/3 (50 weight, 3 ply). "Thicker" thread is often 40/3 and you'll see that sit right on top of the quilt and be a very bold design.
If you use a variegated thread with colours matching your top, you'll have areas of quilting sort of drop out, where the thread colour matches the top.
Love the quilt - very cheery :)