BuddyPress.org

No, you cannot have multiple instances of BuddyPress in one installation. In other words, BuddyPress works in one site of your WPMS install, there’s no BuddyPress multisite script at this time..

1. No, per above. You will need to install one WP site for each BP social network at this time.
2. BuddyPress can track as many blogs as you want. It all depends on your server … and tech skills of course.
3. See #1.
4. See #1
5. See #1. Wait for BuddyPress MS plugin or create one.