I agree more or less with the previous suggestions. Only one, or maybe 2 of the 4 branches will be your finished tree. If you want to get the "best tree possible" out of this tree, don't rush. Plan on taking your time. No cutting until after you have made a drawing or two, or a photoshop mock up of what you can see as a future tree. When you cut, leave long stubs, these can be stripped of bark and used to create jin - a deadwood feature. Initially leave the long deadwood, you can always shorten deadwood later, it is tricky putting length back on to deadwood.
If it were mine, I'd probably plan on repotting in spring. my main concern is to keep the root system healthy, and since you don't know what it is potted in, it might be good to get it into a bonsai pot or an appropriate shape bonsai training pot. None of the the trunks looks like "Cascade style" to me, so I figure it will need to fit a normal bonsai pot. Most bonsai pots are less than 3 inches in depth, with 4 inches being the maximum depth for pots that are not custom pots. SO fine a nice production grade bonsai pot, or plastic bonsai pot that is 4 inches or less deep on the inside, and do the root work needed to get this tree into that pot. Ideally the new pot should hold almost as much media as its current nursery pot, but be low and wide. This will allow better development of the currently quite nice nebari.
Because you will be repotting in late spring, do no pruning now, and no pruning until after you see good foliage growth after the repotting. You want to let the tree have at least one growing season to recover after repotting. You might get away with taking off one of the 4 branches, but don't take more than that before repotting. Then your next work session should be sometime in 2021 if you repotted in 2020.
Remember Junipers are last on the list of trees repotted in spring. They are best repotted late spring. Some, including myself repot junipers in July and early August (early and middle summer) too.
Use a modern, inert bonsai mix as typical for conifers. Some blend that includes a significant percentage of pumice would be good. This way you will not have to repot the juniper for 5 or more years. They do not develop well with frequent repotting. If you can keep repotting frequency at once every 5 or more years, the juniper will be better for it.
With the revitalized root system, the juniper will be more likely to bud back. Then when you go to do serious styling, say in 2021 or later, you will have new growth to choose from in addition to the growth that is there.
Of course junipers are tough, resilient plants, you could get away with more aggressive work, but myself, I would take my time with it. During this time, you can see the different options.
