how can I send 3 email notifications based on the status of a task list

I think you would be better off just setting the reminders within the task.  I like to refer to them as "Nag-a-grams".  Now this just works of the function that the task is due the moment it is created.  If you are creating separate tasks outside of a workflow, you could create a site workflow that parses through the tasks library looking for tasks whose status is "not started".  You could do that with a Query list action. Filter the query based on status of "not started" and collect the fields of  "assigned to", "title", and "due date".  You can collect other fields you think will help.  You will need to do a calculate date to determine what date is 3 days from today and yesterday's date.  That way you can evaluate those calculated dates against the due date.  Then just run some run ifs to send emails to appropriate person.