English Insitute app

We are in search of an APP for our English Institute. (It is not a learning app)

For who:
English Institute that provides online classes

Needs:
We have 200 students and we need the app to:
1. Record students attendance and keep live attendance % at all times
2. Be able to send push notifications to remind students of class
3. Be able for the student to access class material from the app
4. Be able for the student to have the class link to access class
5. Be able to send our students test
6. Be able to be used as a way to communicate with our students.
7. Be able to post information to our students
8. Be able to market our courses to new students
9. Have a pay button

Please describe in how many phases you can develop this APP and what is your Price for each phase.