Damn, I'm like bombing all military references.
The challenge with Negan's group is that they are spread out.
It calls for small-unit tactics.
Now as far as the undead go... the most realistic account I've come across was in the book "World War Z" in which the movie was based and did a ****** job covering.
Anyway, the survivors of the country first cleansed the western edge of the country from the Rockies (and the Rockies northern extremities) to the Pacific Ocean. And they started going east from the Rockies. They'd use dogs to draw in a bunch of the walking dead and then use weapons where the rate of fire is controlled in order to better make the shots count.
To me a low-velocity weapon like a .22 would be just about the perfect weapon. You see the Henry Rifles advertised on TV. They'd be great tools for something like this. Arm 20 people with those and they could wipe out a sizable herd in no time. In the TV shows like "TWD" you see them spraying bullets around here, there and everywhere.