This WordPress plugin is a complete flexible Projekt Task Management System. It's a very easy to use, but yet a powerful plugin.
More information can be found at klasehnemark.com/project-tasks
Yes, you can make many adjustments using WordPress Hooks. Read more at klasehnemark.com/project-tasks
No, the database tables created by the plugin remains intact when deactivating the plugin. The tables are deleted when removing the plugin completely from WordPress.
Yes, however, the Project Tasks Menu in WordPress Admin is only shown in the main site.