NZ, with satin you need to finish all edges as it ravels pretty bad. Also, most satin is not washable (unless it's polyester). It usually has to be dry cleaned. When you press it, always use a pressing cloth and much lower heat setting. And press from the wrong side of the fabric.
I'd use an 80 (12) needle and #2 stitch length.
I used to be a costumer for the ballet! Your dress plans sound wonderful.