My brain is fried from planning, so please excuse this admittedly dumb question.
Can I buy a Roma Pass at Fiumicino when we arrive? Or would it be any easier to buy it now online (certainly not cheaper, but, for whatever reason, easier?)
Any TI office should sell it also.
You can also buy it at Termini Train Station. That's where I ended up buying mine both times I was in Rome. There's never been a line to buy it either.
Yes, you can buy it in Rome, Ron in Rome says you shouldn't bother pre booking that: http://www.roninrome.com/transportation/what-to-pre-book-in-rome
Yes, you can buy it at the airport. You can also buy it at any of the sites that honor the pass. I wouldn't bother buying online as you have to specify where you will pick it up and you may come across something more convenient when you get to Rome. Donna