CMS/Forum/Premium Content

I am currently working on a site which has a series of tutorials on (videos, pdfs and html content.) I have not actually written a line of code for the site yet, as I want to make sure that I can provide great content as well as a nice site.

Anyway the idea is that users land on my site, can view the free tutorials without having to sign up. However to access other tutorials, users are required to sign up and pay a (very small) premium membership. The tutorials are to be sold per tutorial, so a user can buy access to one at a time.

eg

User buys tutorials for topic 'apples' and user then has unlimited access to the entire 'apples' package - videos, pdfs etc.
If the user then decides to purchase the topic 'pears' they then also have unlimited access to that topic.

As well as providing the content, I would also like to provide a forum. Ideally users would have a single sign up for the site, so they can then buy topics and use the forum. It would also be slicker if the user only had one log-in form for the whole site.

I have been thinking about ways of implementing this and have come up with the following:

1) Use a static site for some simple static pages - eg about us, home, contact us etc. and just link from the main site to the forum. In the forum i could have restricted access to certain sub-forums and just manually change the access once i receive payments [unless there is a simple way to automate this?]

2) Use a CMS which has forum module and a restricted access module

Ideally I would like to have all of the processes automated and use the CMS, but is there any other methods that people can suggest? Also can anyone recommend a CMS with these abilities? I have looked at Joomla, and have seen that it has a module for the payment part, but it looks like a lot of mucking around to get the forum integrated properly.

Does anyone know if you can set up a forum software which you can just point to a database where it will get the user information that it needs for a member?

Feel free to post any thoughts on my set up, I read a couple of posts below that a guy is looking to do a similar thing, but don't worry my content is very specific and is nothing to do with computers.