I would remove all of the branches in the spring, in line with what
@leatherback is suggesting, and make cuttings out of several, because you are going to need to do a fair amount of root grafting.
You should always start with the roots and the nebari before you worry about the upper trunk and branches, particularly with a RoR design, since so much attention is being focused on the "believability" of the composition. Right now the tree looks like it is doing the splits on top of the rock. You have two primary roots that are far too large and thick, and not enough secondary and small rootage. The tree has no sense of age or scale... rather, it looks exactly like what it is - a sapling someone placed unnaturally on top of a rock.
I know this is harsh feedback, but if this tree were in a pot (instead of on a rock) people would be telling you immediately to consider an air-layer to get rid of the bad roots. Possible front #2 looks particularly bad... since it looks like you are highlighting a bit of male anatomy
So if you don't want to completely start over, you are going to need to do a lot of root work. That should be your primary focus right now.