The answer (as usual) is... it depends. Usually the entire top is finished before any quilting is done. However, if you are planning to do the quilting on your domestic sewing machine, and if you would have trouble putting the entire quilt through that narrow opening, you might choose to quilt in sections. In this case, you might choose to add the borders after quilting the center. I recommend getting Marti Michell's book, Machine Quilting in Sections, which explains several different ways of doing this.