Members section for a not-for-profit network

Hi WP world,

I’m part of a small not-for-profit that acts as an ‘umbrella’ network for about 100 other not-for-profits. I’m in the process of getting our website up and running and am toying with ways of creating a members section. We’d like to have some of our documents publicly available, but others (like our meeting documents, upcoming meeting dates, training materials and soforth) would be in a members section.

Some considerations:
– some ‘members’ are organisations (often meetings are attended by different staff members from the organisation); some ‘members’ are just individuals
– our internet in this country can be very slow
– we’ll eventually be making the whole website bilingual
– we don’t need any payment systems; just a way of generating logins for all the members/organisations.

Can anyone suggest a good lightweight plugin – preferably free! – or a way of doing this? Any other NFPs or community organisations been in the same boat?

Thank you!