Elgg isn't really set up to support complex file searching by content type or a full blown discussion forum. There is the pages system which supports group pages and you can set up an access group to restrict write access to a smaller group of people than the readers, but doing so is not entirely straight forward.

I suggest that you consider using the Vanilla forum integration plugin and perhaps the Mediawiki integration as well.

For file stuff you can search the plugin repository but you may end up needing to write (or contract someone to write) a plugin to add those features.

So in short, there's nothing in the core Elgg engine stopping you from doing what you want, but I think that you may find that the available plugins focus much more on the social networking features and less on the information intranet possibilities.