Okay this is my current Bangboo strategy.
Goal 1: acquire 3-star Belion, this is the breakpoint where he gains new ability to only require 1 Yunkui member. Achieved.

Goal 2: acquire 5-star Robin, this will make him really good for Astra-Miyabi-Vivian, since he can also trigger Astra's 4th Kaboom stack.

Goal 3: acquire 5-star Snap, will be useful for any 3rd team I cook up.