Hi. i read your requirements you want course study app where user can buy your courses, i will make it through firebase where you can upload your courses videos then you can change them or delete them and edit them, then people can only review those videos if they buy your courses. your app will be exactly as your requirements.
i will complete this app in 10 days. kindly contact me as its starting of my profile. i will give my hundred percent. kindly text me.
have a good day.