PHP date calculation and simple MySQL query

I have a MySQL table with about 25k users and growing. A part of those users pay a yearly fee to use our service. During the first few months of 2013 we used Paypal but later switched to a different creditcard company to accept payments. So we have 2 extra fields in the userDB: PayPalPaidDate and CreditCardPaidDate. PayPalPaidDate had the date and time in this format: 2013-01-05T06:07:55Z and sometimes also: 18:37:09 Jan 19, 2013 PST. The PayPal API did that. CreditCardPaidDate has the date and time in this format: 30-05-13 22:41:22 (This is the European standard as in: 30th of May 2013 Both string can be easily converted to Unix timestamps with PHP5 strtotime, I tested that already. So I need a PHP script which can be run as a cronjob every day which grabs all users who have a certain type of account role (6,7 or 8 are paid accounts) from the MySQL database and then calculates if the paid date was over a year ago. When a year (or more, some account have already expired) has passed it should clear out the paypal and creditcard paid dates in MySQL and reset the account role to roleID 1. It should then send out an e-mail to that users about this action. (I can supply the HTML and Plain Text for that). The second thing I need is a script (or all in one script, thats up to the programmer) which sees an account is about to expire in 28 days (4 weeks) and sends out an e-mail to that user saying they need to upgrade or their account will be reset to normal as of date xxxxx. It should do this 4 weeks in advance, 1 week in advance and then 1 day in advance. Users should never get more than 3 emails and the fourth being the expiration e-mail discussed above. I need to run this script as a cronjob so it's vital that users do not get bombed with emails everytime the script has run. So the script has to check if If you need more info please contact me!