You may even want to use two layers of a soft batt to get the right amount of stuffing. I like the thin denser batts that are easier to trim. The newest batt I have tried and loved is Quilter's Dream Poly, in the mid-weight. Small needles make small holes, and holes can cause so much trouble in machine quilting. In my last quilt, I used 2 packs of needles just for the quilting.
Universal needles are fine for piecing.
The thin thread is much less noticeable than thicker thread. For tiny stippling in the background, you need to use very fine thread and a fine needle. Try some of the new RJR or Kaufman cotton Sateen - it looks beautiful quilted, is soft and drapey, and has a nice sheen even after washing. Comes in many solids, including a soft muddy mossy green. I take several very tiny stitches and gradually increase the stitch length to where I want it to be, and then cut off the tails right at the quilt so there is no visible thread left.