If you want to work as part of a group or company, I think you're good to go. If you want to work independently, it would probably be wise to acquire some knowledge of at least one common small-site content management system (Wordpress, Drupal, etc.) so you can create sites for your clients from scratch. (I favor Wordpress, myself, despite the occasional antiquated code in places.) Having worked with the S2 templates, you're actually pretty well set to look at the Wordpress theme system, for example, and see what it's doing and move bits around.