I don't know if it's the same as other freezers, but usually the higher number means a colder temp. I would put it as cold as you can stand it for your other things (like ice cream, etc.). But I would have it as cold as I can stand whether there was breast milk in it or not. Mine isn't a Kenmore, but my freezer has settings 1-5 or 1-6. I think mine is set on 4 or 5.
Simply the fact that it's a deep freeze is good enough for your milk to be in great shape. Deep freezers don't get opened as often as everyday freezers, and because they are chests the cold air is better able to stay inside. Those things alone enable them to stay colder and regulated temp. As long as things are frozen, the temp at which they are frozen shouldn't really make much of a difference to their longevity...I think.