So with the village lots being given out soon, instead of buying a village sized house: If I left the lot empty, could i just place an npc building on the lot and use that as a house? Like NPC guard tower, etc.
Yes. Village Lots and bigger allow you to just place the lot on land, and just start adding deco. Don't even have to place a house. That's how many of the garden areas in the game are made. You can't currently do this with ROW lots though. But this option will be available in the future. Such as, you could make a Row Lot garden. And have no house on it.