Question Graphics Resolution for UI Screens - Pixel Art Game

Basically I was working on Pixel Art 2D game and we have used Reference Resolution 480x270 pixels.
This is working properly and I have completed few levels of the game but now its time to create different UI screens for the game.

In creation of UI screens, I am confuse with these questions:

• which resolution graphics I have to use?
• which size of UI Canvas we have to create?
  
• Also sprites shall I have to import with 48 or 100 pixel per unit?

Overall we have targeted 1920x1080 resolution for the game but because of Pixel Art style we have used reduced version of sprites.

Please share your suggestion regarding this.

 

Please someone suggest me something for this because this is my first pixel art game so regarding UI I can't able to take decision so your one line of suggestion give me a lot of help