Notifications Questions

Morning (to those in an appropriate time zone),

I have three questions for you coders out there:

   1. How do I schedule a notification that is not one time, so that a user does not have to run an application     to receive the same notification after X period of time. From what i can tell, its only a one time thing and the application has to be opened again to reschedule the same notification

   2. My code sometimes (more often than rarely) generates two of the same notification twice, is this a known issue or did i mess up somewhere. 

  3. Is there anyway to stack notifications (for android) so that all the notifications for my application fall under one category?

Cheers