1. Facebook connect is currently done through a plugin called "Social Connect"
http://wordpress.org/extend/plugins/social-connect/. Mailchimp integration is not yet a feature either of the plugin or of the theme.
2. No default option on this and can either be implemented through the use of WPMU or through subdomain installs for multi-city setup. This may require further code customization depending on your additional requirements.
3. The theme is not encrypted and so you can definitely access its codes for further modification.
4. Refer no 1.