How should I go about implementing a website that contains tutorials?

I want a website which will contain the following
1. Freely accessible course materials on various subjects, such as Physics, Mathematics etc.
2. Each subject can be divided into different sections, sub-sections etc.
3. Content will consist of text, audio, video.
4. Students should be able to easily browse through the course materials.
5. There should be good search facility.
6. There will be registration and login facility.
7. One of the categories of users will be Authors. Authors should be able to add content and also edit content previously added by them.
8. Students can login and get one on one tutorial from a tutor.
7. There will be quick chat box.

My question is -
Should this website be implemented from scratch using css+html5+php+mysql+javascript+ajax? Or should I use some tools, such as WordPress, Moodle, Chamilo or some other? If I should go by tool, which one do you recommend?