UI/UX Deliverables for Unity Game?

We are making a game in Unity and was wondering what should we expect beyond Mockups, UI Explanation/Implementation Docs and Icons/buttons from the UX artist to give at completion to the Unity Developer to implement the UI in the game.

  • If an avatar is on the screen? Do they need to submit sizing dimensions for the avatar or does the Unity developer just extrapolate from the mockup?

  • Do Font sizes for text need to be specified

  • Since buttons are sent as images, does the sizing of the buttons need to be specified for the screen?