The tiny stitches were probably caused by the presser foot pressure being too tight over the seams. You probably want pretty loose presser foot pressure so the feed dogs can still move the quilt even over that bulkiness. I think there is a lot more risk to having the pressure too tight than too loose, so I wouldn't be afraid of loosening it too much. You can make tightening adjustments as you go if you see the need.
You do not need to iron the quilt sandwich after misting with spray starch. Drying between layers is enough. There is no harm in pressing the quilt sandwich with steam after starching; compression is good, as it makes the quilt more manageable and easier to go under the presser foot. However, I would advise pressing only if your batting is cotton or wool and not puffy. It's fine to press if the batting is Warm and Natural, for instance, as that is a primarily cotton batting (only the scrim is polyester) that is very stable and not puffy. A polyester batting could melt under a hot iron. Puffiness would make it too easy to press wrinkles (future tucks) into the top or backing.
If you loosen the presser foot pressure, spray starch both sides heavily with several layers, and are careful to position the quilt before sewing so you can feed the sandwich to the presser foot from above, I think you will be much happier. If you run into the problem of tiny stitches again, my advice is to immediately stop sewing, because there is something wrong and you do not want to have to rip out those tiny stitches again. If it happens only occasionally, you might want to try lifting the presser foot and manually moving the quilt sandwich, taking a single stitch at a time, until you get past the problem area.
It's also better to have a slightly longer stitch length, as others have mentioned. Ideal stitch length depends on your batting thickness and density. Experiment on a scrap sandwich to find out the longest stitch that still looks good to you.
One more thing. Safety pin basting is not ideal for machine quilting. I ruined a new, very expensive Bernina walking foot with pin basting. I was taking pins out in the area I was quilting and missed a single pin. It got caught on the back of the walking foot and I didn't realize it until it stretched out the spring inside the foot. $150 into the trash. I never used pin basting again. Spray basting is not only faster, it doesn't ruin walking feet!