anything suitable on wpmudev for document management

Hi:
we use standard WP, For our non-profit website. Our legacy document management system was a HTML dinosaur, with no breadcrumbs, tracking, reliable security. Hard to use & update.

We need a closed access solution that allows nested subdirectories, tracking, easy backend updating, etc.
Some of this could be via a wiki, but there is definitely a need for role-based security.
It is essentially a reference database, to be undated by chosen editors.

Most existing documents are in PDF format, and allow 'easy' downloading & printing. Contents ranges from course brochures & user/volunteer manuals, workbooks, some shared imagery & marketing stuff, and more.

It's time for a nimble, full featured solution.
Is there anything we could use within the plugins offered here, or can you recommend what I could look at? We are not yet using a membership system (nor roles), but know this will be required.

Would love to use the Communities plugin for other needs, but that would require a parallel MU site... a stretch for us at the moment.

Many thanks
Peter