1. For the customizer issue, can you please enable WP_DEBUG to show if there’s any error occurs when accessing customizer panel. You can check this article to find how to enable WP_DEBUG http://support.jegtheme.com/documentation/system-status/
2. For the social login plugin, you need to increase the PHP version of your website. You can use PHP v5.4 or higher version.
3. For the template post, since you’re using AutoLoad Post feature, that option will not work because that option has been overridden by Auto Load Post option.