Have to identify the material first. It’s a starter seiju. What style are you interested in creating with it?
You have a junction of the three major branches. That isn’t ideal for starting a tree out. And seiju along with most dwarf species develop bulges and reverse taper easily. So already one branch should go. Unless you want a broom style.
Most young trees grown upright lack unique character to work with, so there isn’t much to work with in that regards. Ideally if you wanted a shohin upright style. You’d want taper and branches starting lower than what you have.
Consider starting from scratch and developing lower branching and more taper, air layering closer to the branches , or doing your best to expedite a tree to grow and start developing what you already have growing. All steps are viable and make sense to consider at this stage. The choices you take early on will dictate where to start and what to expect.
It is possible to make a nice slender tree. A lot of shohin are compact and have at least an inch trunk near the base.