Hi,
I will try to answer you questions:
1. I am not sure if there is a check-in check-out facility on the current CMS. At least on the core content repository (CR) underlying data model does not seem to support this. There are different publish states however. Also it can be coupled with a workflow, as seen in the current CMS packages. You can either implement this check in check out or make use of the workflow package.
2. There is no actual metadata field. However contents are indexed to a search engine such as the current OpenFTS. You can also classify contents to tree like structure called keywords, but it more acts as a classification system. There is also no stopping you from creating such field and using it as you have said. You can create your own custom content types that has this field and inherit from there.
Hope this helps.
