1: you can delete the names in the field definition in the file list to get read only fields. YOu then would have to edit each field in the tag panel. Also, clicking on any read-only field in the file list ends the edit mode.
2: it has not. You can define more or less any player you like. Playing while editing is usually a bad idea as this frequently leads to locked files.
3: no, there is not. There is a thread dating back to 2005 and some from 2009: /t/8895/1
But you can use the Windows Explorer and drag&drop folders from there.