Thanks for reading my comments. :-)
I think what I said covers most (all..? ) of those points (maybe).
I was looking at the Scheduled Mail settings. I wasn't counting days ahead but considering actual dates. So if you want quarterly reminders you just set four reminders up for the year (four, I can handle as quarterly is a bit of an exception..! ). Lets say January, April, July and October. Pick a day but never 29th, 30th or 31st..! ...and set the Year to 'ANY'. So on one day of each quarter you get a message going out every year regular. You even get to customise for the actual quarter as there are four messages set..!
It's a small price to 'pay' not being able to have 29th, 30th or 31st..!
(..and I think doing it like this, most of the code is already there.)
If you want one, two, three etc. weeks notice then just look up the date of that reminder for one year and set up the message. Set the Year to 'ANY' and your done. It would go out on that day each year.
Set up a message and set the Month & Year to 'ANY and you have monthly reminders regular.
Only small limitation is never use 29th, 30th or 31st..! (Although there must be some perverse situation where you want to only send out a message on the months that have 31 days..!)
The coding for this seems simplicity itself for DW (see, I do think of these things).
When checking for Month, accept 'ANY' as true, and the same goes for Year.
The only other part is that if Month or year is set to 'ANY' then don't remove message after sending. (Well, it sounds easy to code, anyway..) :-)
DW could fit it in during a coffee break.. ;-)
(Oh.. DW, I don't think I know of another system with this feature... yet)