I think that it's a good idea; I've considered doing similar myself. Since you have potential local customers, that would probably make it a little easier. Then if and when you get enough of a following it would be much easier to get a small business loan and build up a brick-and-mortar shop/teahouse.
As stated, you're going to have some stiff competition online, so you'll have to be able to offer something that the others do not.
Just remember that most of business is psychology. Surely you already know that with your background, but I suspect that being a sales person for another company with an existing reputation is a bit different from starting over with your own. Until you get some kind of reputation you probably won't make much money, if any. Of course having zero overhead will help that considerably - the worst case scenario is that you end up with a bunch of tea that you have to drink yourself
Here's a great book about marketing/advertising posted online. It's an old book, but a very good one -