[webmaven]

It sounds as though a customizable CMSm or DMS would be just the thing to take care of the fiddly bits that trip up developers of de-novo solutions (ie. accessibility, internationalization, usability, binary format document storage and indexing, access control, etc.). My personal favorite in this space is Plone[1] which has an excellent security record and happens to have many EU developers, but most of the popular contenders will do as a starting point.

Enterprise intranet/extranet apps often start out small and then spread like kudzu, eventually prompting a major project to replace them wholesale with a huge consulting-ware solution (like Sharepoint) that never fulfils the promises made (The exception being the specific niche you're asking about, compliance, which does have proprietary solutions that work, but are incredibly expensive).

To avoid that fate, try to pick something that you know can start small but you have evidence that it can also easily (ie. without a huge consulting engagement) scale to an organization-wide solution with 3rd-party as well as in-house extensions.

Good luck!

[1] https://plone.org