I haven't played the game and i got the 48 notice on the KS so i've been watching videos. It seems to me that starting with a monster just delays the meat of the game. It that a rule that always happens in setup or is it dependent on the scenario?
The introductory scenario doesn’t start with one. But all of the others do. Thematically, you pull up to the next “area” in your van. And naturally your van makes noise and attracts enemies.
As for the expansions, I don’t know if they’re the same.