Creating a calender that automatically lists which events need to happen on each day

Hi

I need to create a calendar in excel that automatically tells me which invoices need to be created on what days.
The invoices are for different clients all of which have a different period between each invoice - this is easy for some as it can be 1 week or 2 weeks, however we also have to raise them on every third Wednesday and other such periods.

I need to be able to create a calendar that automatically recognizes what invoices need doing on which days for at least a year in advance.

I also need to be able to use a macro to automatically insert a new client and have their invoices added to the calendar automatically so my colleagues can use the spreadsheet as well.

I have made very little progress with this so far so any help would be greatly appreciated.