Here is the look with 5 x 7 blocks. The finished size would be about 57" X 75". That sounds plenty big to me. You would need 1/2 yard fabric to make the binding plus 2 yards for the solid black for the triangles and narrow border. Also I was thinking about the construction and particularly about cutting the border strips.

One way to create Piano Keys Border:

1: cut a strip 9.5" across the width of fabric
2: from each strip cut (3) 9.5" squares; that will leave strip 9.5" X 13.5" long
3: cut (3) strips from each 13.5", each 3" wide
4: strip piece all the 3" X 13.5" strips into sets for the border
5: cut each 13.5" strip set into 4.5" long pieces for the border and then piece them together