I would plan on having about 10 yards of the background fabric around. If you're doing paper piecing, it will take about as much of the background fabric as if it were solid. This will of course change if you're doing borders and how big they are. You can do your own calculation of how much would be needed for the solid background size you need. Then for the color(s) of the star points, you'll have to figure this out yourself based on how big the pieces/points will be.