I have done a lot of trial and error to make this rocket work, but now I have finally created the second stage for the full starship rocket. I have tested this in an orbital flight, and it works flawlessly, it is very light on the computer (what I mean is that it gives the normal KSP2 FPS) and it can also land perfectly! (Have only tried a water landing).
This has enough Dv to get all the way to Duna!
This rocket was referenced from Starship SN10.
THIS WAS TESTED WITH JOINT_RI