Just the Invoicing is all that is needed, I've tested sending and receiving.
To receive an invoice in the Vendors - Bills screen there is a option "Fetch e-Invoices", when that is clicked the invoice comes almost instantly after it's been sent.
The only issue I have is that this option is not visible in all Bills screens, if I go via the menu to Vendors - Bills the option is not there, if I go via the Dashboard to Purchases (which I think it's the same screen) I do get the option to fetch e-Invoices
I've not had any "unknown" invoices appear, only invoices from a company that wanted to test this functionality so I'm not sure if after some time those invoices are fetched automatically, if anyone knows it would be interesting to know the interfals.