Normally when I spawn creatures, I do it through the area's On Client Enter script, not through a conversation. You'll never be entering these areas unless it's to fight some newly-spawned enemies, right? So I'd use On Client Enter, like the SoZ areas
If you have the different area types you described before (mountains for ogres, graveyards for zombies), there's no need to use the conversation to decide which ones to spawn. Each area itself spawns the appropriate creatures.
Or, you could use the built-in encounter system. You populate the encounter list with variant creatures, place special waypoints around the area, and a trigger. You can fire the trigger via script (such as in the On Client Enter script) instead of making the player walk into it.
For the level-appropriate creatures, you'll need to either make or import creatures of the levels you want, if the toolset doesn't supply them.