If your image frame size is 60x60, 1x image should be 60x60, 2x should be 120x120. And 3x should be 180x180. There are tools in Mac App Store which lets you resize the images to desired sizes so you can resize multiple images at once. You can see this article to get an idea flow about how to create 1x, 2x, and 3x images: https://mic.cognirush.com/optimizing-your-website-for-all-screens/ It's written for web-sites but you can also apply it to get 1x/2x/3x image required by the XCode as well.

D-U-N-S number is for businesses. Individuals do not get it.

Yes, better communication would have saved some time in my case also - my application was rejected multiple time and once the issue was corrected, my application was approved. I haven't heard people getting banned due to multiple rejections.