BuddyPress.org

@mgelblum Many things in your post are do-able with BuddyPress out-of-the-box and with additional customizations and plugins which are free and those which are paid for. And then it also depends on your server and your ability to go through with the project or might need to hire someone to do.

As for the Sansation theme, either add BuddyPress Template Pack or port Sansation design to your own BuddyPress Child Theme. Either way, you need to have HTML/CSS skills with knowledge of WP/BP template tags.