@Mazen Regarding your first question, are you referring to data submission or data display? If it's the latter, you can simply wrap the output of the extra field you want to hide in an if statement that checks user permissions.

As for your 2nd question, there are many ways to do this. The simplest though is with Simple Image Gallery Pro (www.joomlaworks.net/extensions/commercial/simple-image-gallery-pro) and some K2 item.php overrides to show the gallery first (in place of the main K2 image).