Sashing with cornerstones would be the easiest. Love the colors you used for your pinwheels!

I would say sashing with cornerstones, then a border. Looks great!!

I would sash them with cornerstones made of smaller pinwheels.

I use sashing on nearly all my quilts. I LOVE cornerstones because they simplify the sashing if the strips are not long enough from either WOF or LOF; often I put another cornerstone in the middle of the sashing to give even more length.

I love your fabric combinations! Sashings with cornerstones would set them off.