I press seams to the side, not open. When quilting over seam allowances, you can use the thumb of your top hand to press down on the fabric above the point of the needle as it's coming back up to the top- this helps control the length of the stitch. If the seam is just too bulky, stab stitching works- just push the needle straight down all the way through the fabric, then use your bottom hand to poke it back up where you want the next stitch to start. Over time, as you practice, practice, practice, it will become second nature. And yes, you sure can use stencils, etc. to make different quilting designs!