BuddyPress.org

bbPress the plugin is still in beta, so I wouldn’t install it in live site. The Lead Developer of BuddyPress is the same Lead Dev for bbPress so you can be sure it will be made fully compatible in the near future.

As to your first question, groups has around 4 tables so I suggest you leave them be even if you disable the groups. As always, before making drastic changes, backup DB and server files.