How can I properly duplicate Fields on entities?
One way of doing this is in the theme layer. In this approach you don't need to have two fields. You could have a single Images field, and in a node template preprocess function you can break it up into two separate variables that are provided to the *.tpl.php file. So you could take the rendered output of the first image, put that in one place, and the rendered output of the rest of them could go somewhere else.