Well, I would say that you can use any sized square that you would like... some quilts a 12" others you may want a 4 inch block...it is whatever size would work best with what you have in mind.
You cut them according to what looks good with your eyes...rotate the ruler back and forth and find the place that looks good to you.
I would think that you could take scrappy one step further by cutting your block diagonally and then sewing the diagonals together... or cut them into rectangles to use as is, or sewn together... Cut them into 4 patches... In diagonals with a solid fabric.... Whatever and wherever your imagination takes you :wink:
Take the scraps and sew them into smaller blocks for the border???