students get a welcome message when they go to a new course. The welcome message is a standard text defined in the lang/en_utf8/moodle.php Students added by teachers as students in courses didn't get such a message and it is not possible to define individual messages for each course.
It will be good to give the teacher the option to create an welcome message individual for the course.
1. new field for individual welcome messages in course settings. If the field is empty the standard text is used.
2. option to send this welcome message to all students that are added to the course by the teacher.