I use a size 14 needle when PP and have a 1/4" seam allowance. If going smaller, I did one where the pieces were very small, I switched to a Microtex needle 80/12 and 1/8" seam allowances. I still used a 1.5 stitch length. As far as using your rotary cutter, I think it's a good idea to switch out your blade after each project is done. With PP, you use your cutter a lot more than you think, one time for each piece you sew on, not including the cutting of your strips or pieces in the beginning and then to square up your block before sewing the blocks together.