There is no need to deque CSS files and JS files from functions.php as W3Total Cache can be configured to combine all CSS files into one and later it in minified.However you must keep in mind that all CSS and JS files are combined serially(one after another , so you load them as per your theme requirements) and then minified into one.
Google fonts are not served from your own server,so, you can’t really minify and concatenate it.Also, Googles font servers are probably faster than if you’d host the fonts yourself.