Welcome to the forum! Always good to see another New Englander.
Re: local bonsai resources- There is New England Bonsai Gardens in Bellingham- a bit further from you than Bonsai West in Littleton but very much worth the drive if you can make it. There is a club there that usually meets first Saturday of the month if you'd like to check it out.
I believe there is another bonsai club that meets periodically in or near Topsfield, though I have not visited them personally and am not sure of their schedule.
Also for what it's worth Brookline is zone 6b according to the latest USDA maps, a bit colder than 7a, though your local microclimate may differ of course.