If you start with 5 inch squares and cut them in half on the diagonal, sew them together you will not end up with 5 in HST. They will be 4.62". You lose .38" in the seams when you cut a 45 angle. Then if you sew those squares together you will loose another 1/2 inch in the seams all around. Your finished block will be 4.12". If you round that all out really your blocks will be 4" square. And the points will have to finish at 1.3" meaning the triangles will have to be cut at 1.68". So charms maybe not a good choice for this block.
