1. I think that yellow flowers will look great, I am not so sure about yellow and ornge. 2. Yes I would add a dark purple shashing and bind it with the same dark purple. Also you might think about putting a yellow block in the center of your white X's on your top. That would bring your yellow in the center of your quilt, although it will look good without it. 3. If you use a darker background than your applique peice it will usally bleed through. You might want to use the white background for the flowers and put a 1" sashing of purple around the applique blocks. What ever you chose to do it is going to be a Beautiful quilt. Lynn