If you look at the highest branches (upper right) you will notice the way the growth looks. This is the way you want the rest of the tree to develop. You need to fertilize vigorously and perhaps think about planting the tree into a colander for a couple of years and allowing it to grow un-checked for a couple of years. I think there are fine bones present for a really good bonsai in a few years. Just be careful not rush it. You need a lot of new growth in areas where there is little so that you can reduce it down again to more healthy growth.