This is wonderfully detailed information @MarshallA . Thanks for being so thorough.

Could you confirm that the billable item PDFs will be attached to the customer invoice for them to click and view? 

Can I choose to leave off the "Pay Now" button on the invoice? I want to look as polished as possible and not leave any question in the customer's mind that everything flows smoothly behind the scenes without them lifting a finger (unless they want to).

Also, do you know of any software that automates this and integrates with QuickBooks? I've been searching for two weeks including on the QB website and haven't found anything.

Thanks again.