UI

Question 1

Batching UI

Answer 1

Separate UI elements in sub-canvases
UI elements within a canvas with the save Z value
Same materials and textures
Same clipping rect

Question 2

Graphic raycaster

Answer 2

Only on interactable

Question 3

fullscreen ui

Answer 3

disable the camera rendering the 3d scene
hide other covered UIs
reduce the frame rate when possible