I understand my original question was very broad and a bit complex but
in case anyone was interested in a solution then here you go!

It works marvelously.

I built an addin that takes a spreadsheet and configures the raw data
for export to a csv file. This csv file is then used by an external
app named "XL Calendar". This app is available at LJZSoft.Com. It's
a very basic calendar app that creates the user's calendar in an excel
file. The wonderful feature is that it will take a custom "holiday"
file and import it that into your new calendar. By modifying my data
into the format used for the "holiday" file I was able to create a
caledar showing all of my customer due dates. I created a secondary
macro built into my add-in to further format the calendar to allow for
a lot of data to be packed into each day on the calendar.