Baby steps. Don't rush him into socializing just yet. Too many new places, too many new other dogs and too many new people too soon. I'd wait a few weeks until he's comfortable with you before heading out anywhere, unless it's a greyhound group meet.
Making the crate a happy place is a good thing.
Meeting the Boston terrier on his turf set him up for a bad encounter. Meeting outside, on leash, preferably walking will help, although the Boston may continue to be a bully.
Clicker training is good. Do it when he's hungry so you really get his attention. When that "clicks" for him, try tossing a treat in the car and clicking. In out in out in out in out. Car rides should be to somewhere fun like a drive-thru for something yummy.
Pacman will set his own time schedule for relaxing and learning you are his new human. We've had some here who walked right in unfazed to one who hid in the bedroom for months.