OP, welcome to the area.
It's been a few years since I have used Tulley BMW (Nashua, NH) but the facility is modern and, based on my past experiences, very capable. You may also want to look at Turner Motorsports (Amesbury, MA) for mods and/or general service.
In MA there are a fair amount of unmarked vehicles plus the LIDAR. Traveling in CT can be very difficult. Watch your speed there. Some really nice roads in VT and NH.
Will the M3 be used in the winter? If so, frost heaves and potholes can be bad around here.