Advise needed for setting up a member site

I’ve been asked about setting up a site for a sports association, one of the possible solutions would be to use WordPress but since I’ve only set up a number of standard blogs/organizations sites I’m a bit unsure of the best way to do it.

The design suggested have four target groups
+ General public (general information, events, what has happened, etc)
+ Members (internal information, nothing secret but probably nothing of interest to the general public, possible a place for discussion (forum?))
+ Volunteers working in the association (restricted information should only be available to this group, also a place for discussion)
+ The “board” (most importantly is a place to store documents)

I’m currently playing with different ideas/tools for implementing this but I would appreciate any ideas, pointers, etc on how to use WordPress for this (or parts of this).

The number of members is in the range 200-1000, depending on how they are counted/allowed access. My guess is that “active” members on the site will be around 200-300 with only 20-50 actively taking part in discussions and less than 10 creating content.