Welcome to our group. your juniper looks healthy, over the several years you have had it you got the basic horticulture down nicely.
That is a nice juniper, most probably Juniper chinensis, there are many varieties of this juniper, Shimpaku is the most common. Read up on Shimpaku as bonsai. Lots of info on web and in books. Hard to tell which variety of J. Chinensis you have from photos.
I would first repot the tree. Don't do any cutting, just repot it, to get it a stable growing container. You are in zone 5b. You need to repot before August 15 or your tree won't have time to put out new roots before winter. Make repotting your first priority. If you can't resist the idea of trimming foliage, do not take off more than 10 % of the total green within 12 months of repotting. In zone 5, junipers do best with only one major work done per year. In zone 8 you can get away with a lot more, but up north only one insult per year rule is best.experienced growers can do more, but you are new to this, if you go slow, the tree will live.
Save pruning for next year or even later. The tree needs the foliage to force the roots to grow.
In 2016 you can do a light pruning. Better to let it grow out. In 2017, after you have a good root systen, and vigorous growth, then you can do a major styling and hard cut back.
Remember, with all junipers, you must keep some green on a branch. If you prune a branch and remove all the foliage, that branch will die.
you have a nice start there, get a pot and pot it up. Buy a good grade of bonsai mix. Internet Sources will work if you only have a few trees.
