Some quick answers to your long list of questions. :wink:
1. Labs 3 Stable, is free can be used for production and many do, however many people also want the guarantees and support that comes with Alfresco enterprise.
2. Not fully sure what you mean by "dynamic content" but alfresco has a range of interfaces for adding content including by email.
3. Alfresco has its own permissions model. Permissions are not at the database level. There are also rules and workflows which can control how content is apprroved or publised.
4. Alfresco is a high performance CMS. Its not really comparable to Joomla (in fact there is an integration between Joomal and Alfresco.) And is not a php CMS either.
5. Alfresco is easy to administer once you understand it. There are many extensions and add ons.
6. Alfresco is multi-lingual and has a bunch of language packs. However if you are creating a website using Alfresco WCM you are free to use whatever technology suits. Alfresco WCM does not tie you into any technology.
7. Meta data is stored in a DB. Content is stored on a file system.