Enrolment

1. Most enrollment plugins let you specify a duration.
2. The plugin enrol_coursecompleted let you add a role to a user when the course is completed (read everything about course completion and enrollment before implementing this). However this plugin does not remove the original role.
3. Removing submissions and assignments from a student is not done automatically, but an enrollment plugin can be configured in different ways what to do when the enrollment expires: keep user enrolled - disable course enrollment - disable course enrollment and remove role - unroll user from course.
4. NO

A lot of what you try to do is possible, except the automatic removal of student data.  Plugins normally stay far away from removing information (you do not want that someone installs a plugin by mistake and all the submissions of the students are gone).

R