Keep diligent about your branch sizing.
The low ones seem ready to be overtaken in size by the top ones. Once they do it's hard to flip em back.
I am not familiar with rain tree. But perhaps cutting the multi leaves in half at the top will help. Along with letting the lows extend quite far before cutting them back.
Since the lowers will then be getting less ramification then the top, don't be afraid to cut the shit out of the top.
Many a raintree have this problem, exacerbated by improper lighting in winter.
Side and low-pad lighting is highly recommended.
You have a great start. I reckon you can keep it that way!
Sorce