The values for the status field are defined in the bpmModel.xml shipped with Alfresco. You would have to override this model to define additional values. Keep in mind that this field has absolutely no value in most use cases as end-users tend not to set it at all.
There is no way in default Alfresco to display workflow tasks inside of a calendar. You would have to create custom functionality to automatically create a calendar entry when a task is created/assigned, and update the calendar entry when anything changes with regards to the task. Also, tasks are usually of a global nature whereas calendars are always site-related, so you would have to have some mapping in place in which site calendar a task is to be added as an entry.
