I'm not sure i follow this one ? why would it matter in which way the images are organised - as far as i have understood there is really no difference performance wise whether you have 10 sprites or one sprite with 10 frames. am I wrong ?
4. Group Sprites images, layout images, Hud wisely. Don't make a ui where 1 image counts as 1 sprite. all Menu UI should be on 1 sprite object, all game UI on 1 sprite object. If you need ui elements on both. It's ok to have 1 sprite object that exists in both game layouts and menu layouts.