1.If you want to bulk add teachers to courses then see Upload users or this video
2. If you set Activity completion the teacher in the course will see a report of who has finished what, or for assignments for example the teacher can see that assignments need grading from their Course overview
3. The simplest way to mail all students is either from the Announcements forum in a course or from the Site announcements as site admin for all students on the site.
(I'll just move your post to the General help forum)