write a VBA code that before you print it updates the invoicenum to invoicenum+1 (you can also set this to worksheet open function.)
Use the Workbook_BeforePrint for this.
Then Have another macro that calls the print command a number of times (get vba to ask you how many times you need to print then loop the print function for this many times) and attach it to a command button.
Would be good to put a slight wait statement to slow down the printing routine as it may overload the printer queue.
Thank you so much, Peter!