Hi. I've already made a similar sheet, so i have experience. It'd print triplicated purchase orders (legal requirement on my country) at a rate of 2 or 3 pdf per second.
If you want i can also arrange it so excel will send them through email. Though that usually takes a lot more of time per pdf, depending on your internet connection.
Do you have a final design for the invoices, or a model i can work with?