Questions with possible t-shirt business?

I know a thousand other people want to get into this online business, but before I jump in, I want to get a few answers.

Suppose I wanted to open an online t-shirt business... What I would do is wait until I get the orders and then have the shirts mass-produced and shipped to my customers.

Who would I contact that would be able to mass produce the design on the shirts - say 200 to 2,000 at a time - onto various sizes and possible sweatshirts as well, and then be able to ship them individually to each customer?

Would there be one company that can not only mass produce the shirts, but be able to handle the shipping as well? Not to me, but to the customers. If so, who are they and how much do you suppose it would cost for 200 shirts? How much for 2,000 shirts?

If no one knows the estimate of the cost, that's okay, but pointing me in the right direction on how to find a company that can do this would be well appreciated. Thank you.