I suspect that without any sort of funneling of zombies into a choke point, bases are going to get over run pretty quickly. Weapons like UZI is going to be pretty essential and it will make the Pistol and Shotgun completely useless cause of their bad accuracy and lack of area they spray into.
I am not sure if you're looking into changing the weapons so they fire multiple times or what but have to keep in mind how many zombies the player is going to be facing and how quickly each wave grows in size. Cause pistols, lee enfields, and shotguns aren't going to cut it at all.