Honestly I’ve lived here all my life and only ever driven through the towns. the NPS seems to have some pretty good info/ scheduled events. Maybe even some battle re-enactments?

Salem/ Lexington and concord almost certainly require a car. Freedom trail, library and such can very easily be accomplished by walking/ train. Boston is more walkable than a lot of US that I’ve seen.

Late March is usually pretty tame for snow, we have for sure seen snow that late in the season but it’s rare. I would bring a decent jacket for sure, cold wind here can be crazy. Have fun!