@T_Thomas - Boston mid-March will be cold / blustery - be prepared for that! Boston is a very walkable city with plenty of transport options (T is easy/prevalent - get a Charlie Card) that don't include needing to rent a car (your call though - parking is always a challenge and pricey plus it's too easy to get headed in the wrong direction for those unfamiliar with the city - it's not a grid, it's haphazard). Uber from the airport is generally the easiest way - cabs can be tricky there, although plentiful there's a few suspect operators. Uber pickup is in the garage - there's signs all over the airport to help you (it's one place you will find signs in Boston).
Northeastern's baseball field is essentially on/off the green line - there's a couple of options - use GoogleMaps to see, but the "C" and "D" green lines will get you close. Where to stay depends on your budget - obviously the closer to downtown & waterfront, the more expensive. You'll be close enuf to Fenway to take a tour and there's plenty of history if that's your jam (Freedom Trail, Haymarket, Old Ironsides). We found the Boston Tea Party ships to be a bit of a tourist trap... Like Canoli's? - Be sure to head to the North End on Hanover St where you can determine if you like Mike's Pastry's or the Modern Pastry (bring cash). Dinner in the North End is an Italian smorgasbord - reservations at some places, while others you will see lines out the door. Plenty of places to find lobster - they'll all say they're the best. Chinatown has a few good places. Use the Open Table app - it'll help. Oh and be sure to say hi to Mike Glavine (HC of NE) - he coached my oldest son's travel baseball team ;-).