To add your Google Analytics tracking, you can add it to the wp_head hook in GP Hooks, or use a plugin like this: https://wordpress.org/plugins/google-analytics-for-wordpress/
As for those errors – are you noticing they’re happening only on pages, and not posts?
If so, that’s because static pages don’t typically display the author or the date. Those tags are generally reserved for posts and other content that changes frequently.
Pages are static, and usually don’t display that information.
Let me know if you need more info 🙂