Hi,
1) Any user can purchase the course but the user will never become the instructor of that course after purchasing.
You have to register user as an instructor in the website and then the user can create courses in the website.
2) You can create batches and then connect courses with it , you can refer this playlist for tutorials on it:
https://www.youtube.com/playlist?list=PL8n4TGA_rwD8C5pJOE7H2Cz_d8kVnCLYQ
You can also use buy batch feature to let the companies purchase the batches, refer:
https://vibethemes.com/documentation/wplms/knowledge-base/wplms-buy-batch-feature/
3) As mentioned in point one, user who purchases the course cannot become the instructor of the course, so you need to register those users as instructor and then the user can create the course and add the content in it according to their requirements.
4) By dashboard do you mean the dashboard in profile ? If yes then you can edit it from wp-admin->appearance->widgets, edit the student sidebar and instructor sidebar accordingly.
If you are referring to course, then the student can only see the course page and the course status page but the instructor of the course can see the admin course menu and from there the instructor can control all the students inside the course.
5) Yes the instructor can connect the memberships or subscriptions with the course and the users can then purchase it.