>If it's your first car, best to have it towed, or let it sit there until you get plates.

Too expensive. Best to simply make two trips. First trip you buy the car and get the signed title. Go home without the car, get insurance who will generate the form you will need to then take it to the registry to register the car where they hand you plates. Now make the second trip out to the seller, put the plates on the car and drive it home.

Alternatively see if the seller is willing to drive the car to you when you exchange money and title. Then they can park it in your driveway, take off their plates, and leave.