When you're considering the number of inflatable outdoor holiday decorations you should buy, there are two main things that you need to think about:
How much room you have in your front porch and front lawn area. Having a large number of inflatable outdoor holiday decorations may be fun, but you definitely need to be able to still access your front yard and be able to see your home from the street, for safety and practicality.
You should also consider the nature of the inflatable outdoor holiday decorations you're looking for. If you have your heart set on a realistic Nativity scene, you'll need to buy at least three inflatables to make it recognizable. If you want Santa and his reindeer, you're going to need to buy several! If you're looking for standalone inflatable outdoor holiday decorations, stick to themed inflatables that don't require accessories or other elements to make the scene make sense.
If you've decided to purchase more than one inflatable outdoor holiday decoration, you need to arrange them in a way that makes sense for the story they're trying to tell, and you need to make sure you don't block your view from your home.