Because the one new fabric is a directional print, I would cut a wide strip of that and add it to the top and bottom to make up the length. Then add the gold & navy borders. Here's a tutorial on how to miter:
http://www.quiltingboard.com/tutoria...rs-t21057.html
Personally, however, unless you really want to sew multiple border strips together before adding them to the quilt or there's a border print you want to showcase, you won't really see the miters and for me it's a hassle. I would add the gold & blue borders individually in the usual manner.