Concrete5 - Automatically email notification when removed from group

Hi I've running a membership website via Concrete5 CMS via the standard group setup. I use the automatically remove user functionality, where the user is removed from a specific group at a certain date. What I need is to be able to send out an email telling the user, that there is X days until the membership ends. E.g. 14 days, 7 days and 1 day before removal. The code should work on a standard Concrete5 installation and use cron job for checking. So here's what needs to be done: 1) Must be made as an concrete5 add-on (package) [login to view URL] This way I can install it easily on my other server. 2) Hereunder I should be able to define: - the specific group it concerns, either via drop down of the existing groups (preferred) or via a text field, - multiple intervals for sending out the mails, e.g. 30, 14, 7 days etc. until a user is removed from the group. I have created some test groups, where I have specified a date for removal. This is the date field which it should check agains. So 30 days means, that the system sends out an email 30 days before the user is removed from the group. - Email Topic Text Field - Email Body Text Field (if WYSIWYG editor if possible, please enable this feature) 3) It needs to run via a cron job, so the server automatically sends out email. I guess this will be a file somewhere I call via a cron job. It should be pretty simple, as Concrete5 handles automatically notifications a lot. Thanks