I dont raise it above 4x until im stronger. even if you max your starting attributes you cant do 30x… trust me.
you can raise the zombie multiplier after you generate a world and while you are playing. as long as you have a vehicle, extra gas, guns in vehicle, and cool explosives, your fine with massive zombies. since you can blow them away and your car is fast enough. I do recommend a rather large car at 30x… you have to drive through alot of zombies.
one thing i am experimenting with is construction. something to funnel zombies through that doesn’t burn. so something with metal. then drop wood and light on my way through. game doesn’t provide much in the way of options to fires going though. for example, if i pile up wood, that doesn’t really work to well to keep it burning longer. also digging pits in this funnel will slow them down so they burn longer.