When I put in a zombie spawner sometimes only one will spawn and that zombie has a gun. Then after I kill it the rounds keep going without zombies spawning. But then other times zombies wont spawn at all. What do I do to fix this?

I was looking at the customization screen and there was some stuff in there that wasn't in the challenges listed. For example the Capt. Price character was there but there was no explanation on how to unlock it. How do I get some of these things.