Can I mine out a big dark place under my village for mobs to spawn in rather than the unlit areas up in the village?
Solution 1:
Having a large dark area — such as a mob farm — is a good way to decrease the spawn rates elsewhere, which is particularly useful when you've explored and lit up all the caves in an area (which will tend to concentrate the monsters in any remaining dark spots).
However, it will not ensure that no zombies ever spawn in your village and attack your villagers. And monsters despawn when you're too far away, so when you approach again, if the village comes in range before the dark area does, monsters will spawn in the village first.