Nordlys

Hi.  I am traveling to U.S. east coast with my Thai wife in 5 days.  We're spending two weeks in DC and NY, visiting my friends from int'l school here in both cities.  Now I have a new agenda on my itinerary - visiting an old friend for a few hours in the city of Trenton on our way NY from DC.  

So my question is...

1) does Amtrak allow passenger to get off the train and hop on another as you like or do they only have reserved seats (do I have to buy two tickets, DC - Trenton & Trenton - NY?)?

2) do they have cloak service/lockers to leave suitcases at Amtrak station?  I found out Grand Central in NYC no longer has one after 9/11.  

My wife's passport with still valid U.S. tourist visa has expired.  Is there anything more than the new and old passport that she has to produce at U.S. immigration at the point of entry?