I suspect that the reason you haven't had a reply is because most of what you're asking is quite basic. You know the pseudo code to use because you've detailed it in your second post.
I admit, not everyone knows all the functions available to use and which is best to use where but a little scouring of php.net would do you good.
1. mysql_connect(), mysql_query(), mysql_fetch() and mysql_result() will work for this particular part.
2. date() will give you the current date but you'll need to convert it in to a format that you can compare to 1.
3. Here I would use a switch() in combination with some additional MySQL fetching to pull out the appropriate email body from a database table that you want to send.
4. mail() is the built in php command to send email. It's quite powerful and can be used for HTML and plain text.
Your biggest issue is scheduling the running of the script to achieve the desired results. Obviously it will need running each day to do the comparison.