help with structure for public website with extranet on top

I'm trying to build an application for a nature committee, that combines a public informational website with extranet features for logged in users on top, but I can't figure out the best open atrium 2 structure for this...

• The content structure for anonymous visitors and members is roughly the same, but for every specific public page the extranet (member) users should see extra information and extra options (like making annotiations, discussions, subscribe button,...) on top of the public information. Also registered users (non-members) will in time get access to some extra options to enable public participation in the project.
• The content falls apart in seperate 'chapters' (like 'situation', 'annual activity report', 'nature area's' , 'ecological monitoring'), but some views will need to combine content from various 'chapters', so there's no strict partition of content to make.

• The public content of the whole site together will have to be printable to one book-like pdf, with version control.

• I guess I need a group visitors and a group members?

• do I make seperate spaces for the public content and the additional private/extranet content? or keep everything in one space and use public and private sections?
• do I use (sub)spaces or sections for the 'chapters'?

Any help or hints would be much appreciated!