Great job, increbidle render!
1. Razor wire would be like a zombie fly trap, probably not a good idea, cleaning it would be impossible.
2. Walls would need to be high enough to prevent a zombie stack-up in the event of a mass gathering.
3. As mentioned before you should install vehicle barriers, in the event crimminals try to infiltrate the facility. Make it impossible to ram the walls or gate.
4. As far as location and planning goes, you should integrate the facility by blending it into the surroundings, or creating an oasis effect, by shrouding the walls with small native bush. You could coat the walls to color match them to the surroundings. Building on steep high ground would be benficial, it would discourage any invaders and make it difficult to pile-up, you could solve that issue by raisiung the facility and make a lowered entrance ramp. Just some suggestions. lol