Sounds like a good plan but you are forgetting a few factors. First of all, you need land to grow the vegetables. If you have a spare garden with enough space to start farming its great, but most people live in big cities with apartments. There is the chance to grow some herbs on the balcony, but that is pretty much it. There is the chance to rent a small piece of land at the outskirts of the big cities, but they are expensive and there is a lot of demand for them. Another factor to consider is water prices, as in most regions of the world vegetables need a lot of water to grow. Another thing could be protection against storms or frost. I think growing vegetables on a larger scale efficiently is quite a hard job and will require some knowledge before getting into it.
You are talking about just a single house. But if you consider how many homes and gardens there are in the world for individuals, if we ALL start to grow our own crops, and I mean ALL, like everyone has a fridge, everyone has a bed, everyone has a couch, and now everyone grows their own crops, how little or big depends on the size you have, some have huge gardens, some can do it on pottery, but everyone has a tiny amount at least. That means the whole population combined would make a lot of crops combined. That would be as much as a lot of farmers, even if not all of them equal. At least would be enough to drop the prices a lot considering it all, and would be great.
