Can you limit or control the number of homescreens without an app or launcher on stock kitkat on the Nexus 4? Likewise, is there a setting to lock your homescreen, or would that also require a 3rd party app?
That's pretty much spot on. You can only create another screen by moving an icon to it, and in the same way you can remove the screen by moving all the icons off of it. The stock KitKat launcher doesn't allow you to simply create and delete screens without using the icons. But by adding, moving, and removing icons you can create as many or few screens as you wish. You simply cannot have an empty screen.