Workflow for recording sales to be invoiced later.

[Tim Uckun]

I want to do the following.

Record a sale for a customer. Maybe a few days later record another
sale for the same customer etc.  At the end of the month I want to
generate invoices for the customers that I have sold things to.
Ideally I would be able to automatically email the customers their
invoices. As a fallback I would like to print all the invoices
(hopefully to a PDF printer so I can email them manually).

How do I go about doing something like this?