Walking Dead is a very famous franchise, but isn't the best for a TTRPG. Players would rather some boss with special abilities or traits.
What is the challenging rating of a enemy with only one crossbows, and the same one but with a submachine? If you have played some survival horror as Resident Evil or Evil Within you will notice the difference when you start almost nude and later you have got enough weapons and ammo to become a one-man-army or a doom-slayer marine. What if the PCs can drive a tank? Or to create the ultimate pitfall antizombie trap. What if players want to use killer drones against the zombies?
And I hate belife susspension with the horror monsters, specially no-supernatural undeads.