For Massachusetts, cars will be required to get anywhere or do anything. I live well outside the city, and just getting to the commuter rail to take you into Boston is a 15 minute drive. Getting to the subway is a 30 minute drive. Getting into the city is 45 minutes, not counting rush hour. (Getting to and from the airport via these public transportation options is not difficult, actually. The airport has a free shuttle to and from South Station, which is where the commuter rail comes in on. South station is also a stop on the same subway line as Alewife, the stop that is a 30 minute drive). Between myself and my parents we have three cars, and I can let someone else drive mine and borrow one of theirs without too much trouble. Depending on the number of people attending we will probably still need to rent for transport to/from group events. The local mall and (candlepin!) bowling place are both a little too far for multiple trips.
In terms of accommodation, we have about 10 or 12 futons and bedding to match. Not much in the way of privacy - all the rooms people would be sleeping in would be open. I don't know about local motels or whatnot - I live in Carlisle, Massachusetts if people want to poke around and see what's available.