sashing on top of the minky will not look good. remove the minky.
i beg you. :lol:
go through all the blocks and find the smallest one. find the largest one.
you have several options.
you can add to the smaller blocks so everything matches the largest, or
you can trim back all of the blocks to match the smallest, OR
add to some and trim the others to create a whole new standard size
or, you can lay down your sashing grid, then move the blocks around underneath until you find an arrangement you like, then pin into place and topstitch to fasten.
here's an idea that just hit me as i was writing this. you know those photo frames you can buy with different sizes and shapes cut out of the matting? they're for framing several pictures at once. instead of a uniform sashing grid, you could make something like that from one or more pieces of fabric, lay it over the blocks and move them around like they were photos in one of those frames, until it looks good. then pin and either satin stitch around the cutouts or do reverse applique.