2d sprite mipmaps and performance.

Hi I have couple questions regarding mipmaps and performance.

1. Let’s assume we have sprite 1024x1024 and we select it to use mipmaps. When we will use it in scene as a super small image let’s say 64x64 then unity will use mipmaps 64x64 instead of 1024x1024 and this will increase performance. (GPU is drawing from 64x64 instead of 1024x1024)
2. What if we would set the size of an image using pixel per unit. So let’s say we have image 1024x1024 which is using mipmaps and we set high pixel per unit amount so the image appears on the scene small like 64x64. Will unity then use generated mipmaps and will draw from 64x64 image rather than 1024x1024? Will that works when we set size of an image using pixel per unit?
3. When we are using atlas sprites where I should set the mipmaps thing? On the sprite itself or on atlas? or both?

Thanks for help!