Max Zombie Count?

[Sjustus548]

I had some questions regarding the number of zombies that can be alive at a time.  First off is there a set number or is it just as many as the computer can handle displaying?  I know spawning in with console commands I can spawn in a ton but I'm wondering about naturally spawning in zombies.  After a set amount will no other zombies spawn in until the current ones are taken care of or can they just keep spawning in?  

How does the system handle zombies that are no longer in the general area as the player?  For instance, if we drive from one city to a different city on the other side of the map.  While driving we have zombies spawning along the road the entire trip.  After we leave the area do the zombies despawn or just go into a sort or slumber?  We've left an area only to return days later and have the same zombies in the same locations that we just passed thru, the world was shut down in between trips as well if that matters.  So I'm wondering if the world keeps track of all these zombies that have spawned in.  

How does the number of zombies alive effect the sleeper spawns in buildings?  We've been doing T5 Clear quests in the Wasteland where the zombie spawns are crazy.  We'll notice after a certain point we need to go down and clear all the zombies that have amassed below because the sleeper zombies just stop spawning in after a certain point.  This is what makes me wonder if there is a certain spawn cap or not.