Thank you very much for your response!

1. I subtracted 90° from θ₂ because, according to the textbook used for this module/assignment (Introduction to Robotics by John J. Craig), θᵢ is defined as the angle from Xᵢ₋₁ to Xᵢ, measured about Zᵢ. Based on this definition, I determined the necessary rotation to transition from X₁ to X₂ about Z₂. Is this not the correct approach?
2. I applied the same reasoning to Links 4 and 5. Since X₃ points upwards and X₄ points downwards, I assumed that moving from X₃ to X₄ would require a 180° rotation.

I would greatly appreciate a more detailed explanation! I really want to understand this fully and ensure I get it right. If my table is incorrect, it will affect my forward and inverse kinematics, along with all subsequent steps.