Can I add external js and css via module info files?
External JS/CSS files can't be specified in the info file at all. You need to add them via hooks, typically I use THEMENAME_preprocess_page() for things that need to be included on all pages, or you can use drupal_add_js() in your .module file.

And you can refer to this page. Here you can see how many ways you can add script/css files.