Check with your hotel if it's closer to the Museum of the Science stop (the stop before Lechmere), if it's about the same distence, I would get off at the Museum of the Science instead. I have only drive pass that part of the Cambridge during daytime, looks fine to me, but not sure how it's like at night. I know the road in front of the Museum of the Science is very busy. And you will be walking along the Charles river instead of any side streets. As for breakfast, there's Dunkin' Donuts and McDonald's inside the North Station (not sure that's what you want instead of hotel breakfast

), keep in mind the place can be high traffic during rush hours (before 9:00am, 4:30-6:30pm). Maybe someone from that area can point you some good Breakfast & Brunch place outside the North Station.