1. Yes. If you try to save a file that has been modified by another user or application you get a message stating that the file has been modified and will be asked if you want to load the modified file or save your changes.
2. Not as far as I know.
3. Not, as far as I know.
You can use Subversion or TFS for source control if you have multiple users working on the same document so versions and changes can be managed properly.