Will you be able to knock holes in floors? Maybe covering them with carpets for traps? Perhaps knocking down the stairs and using a ladder to climb through the hole and then pull up the ladder?
Probably not holes in floors, but breaking stairs and pulling ladders are definitely something we're going to be adding.
I have another question, will relative population density of the area be taken into account when determining the number of zombies to spawn in that area? For example, will there be less zombies in rural areas (as one would expect) or will the density of the zombies be consistent between all areas?
Generally, we will use the reasonable density of an area. As a general rule, a city would have a lot more zombies per square meter than a rural area might. But this will also be randomized some, and you may occasionally come across an eerily vacant city district, but a very occupied farm field.