(Arduino) configuration final...
Ah! That simiplifies answering considerably, as your choices are considerably reduced.
Do you need to go through a USB link? No... as I think has already been established.
So how to connect the pins on the Arduino to the "outside world"?
Yes, the circuit given will do it. But why re-invent the wheel? There are several people selling, at no great premium, boards with the electronics you need.
Sorry to keep banging on about it, but...http://www.arunet.co.uk/tkboyd/ec/ec1ser232.htm
.. also has that information.