you do not HAVE to stitch on both sides- that is a personal decision- some people do- some people only stitch on one side (either the outside- or the inside) consistantly. other's stitch right on the seam- the quilting can be done any way you want it- and the distance/density of quilting is dependant on the batting- some batts require quilting every 2" others allow up to 10" between quilting lines- you need to follow the recommendations to the point of quilting at least as close as it says is required. more is ok- less can cause your batting to separate & ball up in your quilt with use & laundering-
so see what the package says you need to do and the decide how you want to quilt with in those perameters.