For me the first question would be how do you want to attach it? If I plan to hand stitch the final side, I sew it to the front by machine and pull it to the back to hand stitch. If I plan to sew it all by machine, I do the opposite.
Strip width varies according to your batting thickness and by what look you like. If you are unsure, cut a few strips about foot long or so in varying widths and pin them to you quilt as the binding would be sewn. Some days it is just easier to look than guess.