Per Bugs:
In other words I need some directions in order to
get a bulletproof and mantainable application from an excel
workbook.

One approach would be to write a user interface using something
like MS Access or .NET.

That UI would manage the user's interaction and make calls to
Excel.

This would also address the issue of bug fixes, since they could
be implemented by rolling out a new version of the application.
--
PeteCresswell