To answer the first question
First, I would like a delete confirmation when users remove an image from the image gallery
You can do that by calling a custom script file from the functions.php.
function alert_delete() {
if(is_admin()){
wp_register_script( 'alert_delete', get_bloginfo('template_url'). '/js/alert_delete.js', array('jquery'));
wp_enqueue_script('alert_delete');
}
}
and create a file named alert_delete.js in the js directory of your theme.
alert_delete.js:
// admin delete check
jQuery(document).ready(function(){
jQuery(".rwmb-delete-file").click(function() {
if (!confirm("Are you sure? This process cannot be undone.")){
return false;
}
});
});