Assuming no EU passport, give yourself 1.5-2 hrs past your arrival time to catch the Malpensa Express (the train from MXP to Milano Centrale) and 20 or so minutes to get on the Frecciarossa from Milano Centrale to Rome. There isn't a train from MXP right to Rome last I checked - there was, but they suspended that service, if I recall. So you'll have to go MXP-Milano Centrale-Roma.

First class has wider seats, generally 2-1 configuration. Second class is 2-2. Otherwise, both have luggage racks and comfortable seats.