Creating a Backoffice For Online Courses

Hello there, we currently need a backend for our course project. We want to offer courses in a specific field and therefore need a login-website where people can register after they purchased the course. In the backoffice you should be able to: 1. Watch all the different courses (videos) sorted by categories 2. Make notes (in some kind of notepad) 3. The website should support video courses as well as .pdf documents. 4. A user CP 5. A payment gateway 6. The option to include recurring billing (once per month) Optional: 1. An integrated forum 2. A chat / messaging system Since the website will keep a relatively low amount of users (every user will pay for the service so you won't face thousands of users in there) the databases shouldn't get too complex. The end goal of the whole website is more or less to over a storage room for all these videos instead of selling them all as pure video files once. Please come up with a short framework on how you might want to do this. We are completely open to any approaches in this, of course we are looking for the best outcome for the best price. We don't care if it includes the absolutely newest technical aspects and stuff like that, because it is a pretty basic thing. I'm already curious about your offers, thanks for your time!