BuddyPress.org

My suggestion (just because that’s the ramshackle way I go about stuff) would be to grab a free BP theme that you like (or just a copy of the bp-default theme), set it up as a child theme, grab a plugin or two that you like, and start messing around with the templates and the css to see how things fit together. I work on an XAMPP install locally for dev, and use Notepad++ and Firebug on Firefox for coding, for what it’s worth.