Simpson,
This is would be a very dynamic oriented script, and a great idea. How I would approach it is first,
calculate how many weeks the user has until there wedding.
Then pull from a database all the steps normally required for a wedding ie.(call the florist, get a cake ect.) then rate them depending on importance and time sensitive.
I would say a very important item would be get a wedding dress. Thus this has a importance rating of 1, and it should be completed 3 months before the wedding day. (I have never been married so I really don't know wedding time frames, these are just arbitrary numbers). But also I would think that equally important (if not more) you need a place to have the weeding. Thus this also gets a level of 1, but this needs to be done before a dress is bought.
Thus order based on level, then date.
Now you will have varying timeframes, ie(3months, 16 months) for planning to occur. Depending on how busy the person is, I would say for anything greater than 12 months you can say that compleeting one of your tasks a week or so would be sufficient, and then base how many steps a week need to be completed based on conditionals.
Hope this helps, if not provide a little more clarity and I will refine my post and maybe others can help as well.
-Farius