Suggest content system for a public information site

Hello guys,

I am developing a website for a holy establishment.

I need the following features:

1. Create(edit, delete also) new posts and pages
2. Taxonomy or classification systen like tags, categories, etc. Custom taxonomy is preferable.
3. Open source
4. Social features like discussion forum - with email notification when reply is posted, etc.
5. Multimedia sharing - sharing images, videos, etc.
6. Abundant free plugins
7. Great secure code

It should be a low-maintenance system, with one-button upgrade feature. I have seen Joomla and Drupal but the code is too complicated for me. The website is not made for money, but to serve as a source of information. Therefore, it is udnerstood that there will be too many contributors over time. Also, the website will also be at time "handed over" to some other person to manage may be temporary or prolonged period, and that person may not be code-literate. Therefore, the system must be easy for any person with basic computer skills.

I am considering Wordpress, but I lack extensive experience with it. I am totally unaware of things like Buddy Press, etc. So please elaborate on this part too.