building an e-learning (e-commerce) website

Hello,

I have two main questions related to each other :) ...

[Introduction]
I am planning to build an e-learning website. There will be several departments (e.g. Network dept), and under each dept, there will be some courses (e.g. CCNA, CCNP... etc). User can purchase any package - let's say CCNA-, either to get DVDs of the course or to watch the course online at two different prices.

[Question 1]
What is the best script/CMS you recommend me for this task ? keeping in mind that registered users will have different access levels depends on which package they purchase. SEO is an important factor. Payment gateway (my next question) is a critical point.
I do not prefer expensive solutions...

[Question 2]
What are the requirements of making online transactions safely. please note that I am living in Kuwait. I want users to be able to pay using VISA/master card and paypal


If you need any clarification on any point, please let me know.