Depending on what bonsai you have, you might plant things to maximize sun or perhaps to provide shade.
Make sure you plant vegetation that wont be disease vectors.
Do you want a consistent theme? If youre going Japanese, think about japanese vegetation. My garden has dwarf pines in the landscape that really add a nice touch. Think Japanese maples, and rhododendron. I think moss is gorgeous and I think moss would make your set up feel more “lived in”
I like your hardscape. I also have boulders. I think they are super awesome in a garden. You might want to think about putting some on the top terrace, or adding those stone Japanese lamps
I personally would avoid vines on my benches as they will degrade the wood and cast some serious shade