Hello,
1) Please check this article or plugin:
http://diywpblog.com/wordpress-optimization-remove-query-strings-from-static-resources/
http://wordpress.org/plugins/remove-query-strings-from-static-resources/
2) Please check this article https://makeaweblog.com/how-to-leverage-browser-caching-in-wordpress/
3) You can optimize images using special services
– tinypng.com
– Compressor.io
– Kraken.io
– Ewww Image Optimizer
– Smush Image Compression and Optimization plugin
Regards