I'd use the plaid cut on the bias for the sashing and binding and then use the other two for borders. You could also use the lt. blue small print for cornerstones between the sashing if you like cornerstones, or a solid gold. I would use gray thread, the color of the inside of the wheels for appliqueing.
I love all those trucks! Your colors and the fabrics are perfect! Is this a pattern I could buy somewhere? What is the name of the fabric line? I would love to make this for my 3 yr old GS.