I like Dario's idea for removing the highest dead wood, then let the rest grow out. Depending on how fast it grows for you, if it were mine, I would do no more trimming, pruning or styling this year or next year. Let it get some growth going. You need to get vigorous grow to cut back into, when you try to style it. If it were mine, I would leave it grow out until 2016 or 2017 before I did any further styling. But then again - I have enough other sticks in pots to mess with that I am currently behind on my summer chores, so it is easier for me to let things grow out. They just get set aside and forgotten about.
That is one cure for impatience with bonsai - get more trees - so you always have something that needs attention.
There are several species of boxwood. The one I have survives our winters fine, no protection from temperature, just under the bench out of sun and wind. (tarps over the bench). We had weeks of sub-zero, and a near record -17 F one night. I know "Kingsville" is not the hardy species. Most boxwood need protection from bitter cold. The one sold at landscape nurseries around Chicago, for landscape use is the hardy one, if yours came from a landscape nursery, or was growing as a landscape plant it will be hardy in your winters - with protection from wind and winter sun it will take your temperatures.