Re: BP Sections?
off hand, two ways to make that happen:
a) You could make each group “hidden” and “by invitation” only. You could assign group admin to send email invites to the site and to the specific group. Since the group is hidden, it will not be listed in any groups directory, and you could always restrict showing list of member to Super Admin only with conditional tags.
b) You would need a separate install of BP and WP for the special sections you want to have. At this time, BP can only be installed once even in a multisite installation. There’s been some talk about a plugin for BP multisite but none have been released to the public yet.