Should we reserve our train prior to getting to Italy or just buy them at the stations at the kiosks?
This is a frequently asked question here, the Trenitalia website does not accept US credit cards (unbelievably, it's true), so it's impossible for those with US credit cards to reserve in advance except by going to RailEurope.com and paying more (a few people here, but not many, choose to do that because they're nervous about not having reservations, but 95% of people here get over it and buy tickets in Italy, your credit card is accepted in country).
Here's another discussion that explains more
Just returned from Italy last Thurs. night. Usually have a rental car and my husband drives but this was a trip with my sisters so we used the trains, ptp tickets. It is really quite easy to buy your tickets over there. Any trains that require reservations, come with the ticket when you purchase it. I printed out the train schedules from Trenitalia's website beforehand with all the necessary info.
I also studied the sample train ticket in R.S. Europe Through the Backdoor so I knew what the words on the ticket meant, i.e. Carrozza means car, Posti means seat, etc. Just be sure to validate (in the little machines) any tickets that do not require reservations. I just validated all of our tickets even the ones with reservations just to be safe. Did see people getting fined on the trains.
Pack as light as you possibly can. We each had a 21 inch suitcase but next time I would go even smaller.