BuddyPress.org

I’m creating a new BuddyPress site that will be primarily organized around Groups. Each Group will represent a city, and each Group needs to have multiple Forums (such as for neighborhoods within the city). Two questions, please:
1) How do I create multiple Forums for Groups? When I set up a new Group, it asks if I want the Group to have a Forum. But it says nothing about having more than one Forum.
2) I’m confused about the difference between a BuddyPress user registration and a BBPress Forum user registration. Do I need both? Does the Forum registration just register them for one Forum, or for use of the whole BuddyPress site? If they register in BuddyPress, do they also need to register to take part in a Forum?

In general, I don’t understand why BuddyPress and BBPress are separate plugins. It would make a lot more sense (and be less confusing) if they were all in one plugin, wouldn’t it?