Do I attach my binding to my top before the quilting is done?
NO. For two reasons, (1) when the binding is attached prior to quilting, the feed dogs will tend to "gather" the quilt top to the binding, thus making the binding smaller than the quilt top, and (2) When the quilt top is loaded onto the machine, the binding is rolled continuously onto itself, resulting in quite a bit of bulk building up in one area along each edge. This buildup creates fullness, resulting in puckers in the finished quilt top that will be there forever.
How much larger than my top should my backing be?
Your backing should ideally be 4" larger all around than your top.