Starching helps prevent puckers because it stabilizes the fabric. Since your quilt sandwich is already layered, you can use some mistings of spray starch on front and backing to help prevent puckering. Lay out a large sheet on the floor to catch any overspray. No need to iron. Just let the starch dry in-between mistings.
Many machines do not handle different colored threads well for quilting. Either there are pin-dots of the bottom color showing on top, or pin-dots of the top color showing on the bottom. It can be impossible to get the tension exactly right to totally eliminate pin-dots. For that reason, I would suggest using the same color in top and bobbin, making it a neutral color, and making it a finer weight so it tends to disappear into the fabric. Check out the Superior Threads website for information.