Jul 19, 2015 - 11:30 AM
Hi Jeristhor, welcome to MySwissAlps!
Basically you don't have to book your trips in advance. But the one to Como could be an exception if you plan to travel on a train that requires seat reservations for the (very short) leg in Italy. In that case both options you are considering will work. But there are local trains from Chiasso to Como too, which do not require a reservation. You can buy a single ticket for these trains in Chiasso, for only CHF 2.
So, the cheapest option is to buy a discounted ticket from Luzern to Chiasso, and a normal one from Chiasso to Como. The first ticket can be purchased in Luzern. The second one probably too, but if not you can get it in Chiasso when you change to the local train.
You can purchase your Swiss Half Fare Card in the US through www.raileurope.com/act ivities/swiss-half-fare-card/index.html or www.raileurope-world.com/pass/swiss-half-fare-card.