First your blocks are cute as heck love the color combo you have going.
Like the sashing, you are talking about adding 30 inches of borders that is a lot, can you make more squares instead? If not how about graduating your borders so instead of 3 borders all the same size do 2" 3" 4" and 5"
or 2" 2" 6" 2" 2" I feel like breaking up the border widths will make it more like a design element and less like I'm just trying to make it bigger. Or a 3" plain border then a piano key border at 6" wide then another 3"
All of your fabrics are so awesome any of them will be beautiful.