You can create a template for the titles and metadescriptions of the tags also in Yoast - go to the section of titles, and then in the taxonomies section, you can create a template for titles and meta descriptions. Scroll down to the bottom of the page - you'll see what you can dynamically insert in your template text.

If you're finding these tags are missing meta descriptions, that means they are pages that don't have meta descriptions. This points to a larger issue - do you want each page being created by Wordpress for each tag you use to be indexed by the search engines? Are these high quality pages you'd want a user to land on? Do they provide value? If not, you don't want them to be indexed. You can use a Wordpress plugin to control indexation of these tag pages - Yoast's SEO plugin, http://yoast.com/wordpress/seo/, besides for being awesome, will control this for you. Install and then go the indexation section, and from there, you can control what is indexed and set the tags to not be indexed.

You can do lots of other stuff with the plugin, and I definitely recommend installing it either way.

Hope this helps and let me know if you have any issues with it.

Google has a program called first click free - basically, you need to allow google bot, along with users, to view the first full article they land on. So if you have multiple page articles, you need to give them access to the entire article. After that though, the rest of the content can be behind a paywall.

You can read more about it here - http://support.google.com/webmasters/bin/answer.py?hl=en&answer=74536

And here are the technical guidelines for implementation - http://support.google.com/news/publisher/bin/answer.py?hl=en&answer=40543

Hope this helps,

Mark