I love your fabric :D:D:D
Increasing your seam allowance to one inch and only clipping within a 1/4" from the seam, when the quilt is washed, the fraying tangles all of the threads and helps keep it from fraying right into the seam. I have seen several that have taken a lot of abuse and no seams have popped yet!!!
Sewing an X in the center just helps to keep the blocks together... I think it is more necessary when you are using a batting than with just cotton blocks. You can sew circles, squares or any other design of your choosing in the center.