First off when you start up the static npc will say something like “Hey I just ate the last can of food we need more.” Then you would go loot the town and stuff then bring back supplies which can be stockpiled in the building. The evac center would be your first base and the npc would use food/ammo/water when needed and helps protect the base. Soon enough you can start getting other people to join you and once the evac center gets too small you can find a new building to turn in to a base.
Now I think if we do this we should also change the number of zombies to reflect the fact that you can have a powerful group come through. Areas should be heavily infested but a single person can actually sneak through fairly easily which would be our scavenging runs. When they want a new base you would take most of the people in your group and slaughter all zombies near a location so you can fortify it.