I would think you'd need some type of permit to open up a shelter? I would check with your county laws to be sure because in most places there are limits to the number of animals you can have. That way you will be within the law and may get some benefits for helping them out!
Find a shelter in your area. They are probably swamped with cats.
You can take the extras, and be a "satellite" shelter for a while. That means you could take advantage of their resources too--access to bulk food, their arrangements with vets... Of course you'd have to run things the way they want, until you have formed your own connections and can strike out on your own. So make sure you agree with their cat-care strategy