Magento order updates automatically

I would like to send magento orde rupdates automatically after a periodic of time. When customers buy products that are out of stock we would like to send them a 1st status email after one week (backorder) and after two weeks a second status (backorder updates). There should be a check before sending out the email (at least one item of the order is backordered). After a month they get a backorder 3 email and after 2 months a backorder 6 email. The emails are already made in Magento and are now used manually.