Welcome to the community. You indicate, "I'm not sure there is . . . a big enough market to support a high-end tea house."
The purpose in developing a business plan (which includes a market analysis) is so you can
be sure before investing your time and money. Of course, a solid business plan will also be necessary if you intend to ask
other people to invest their money to help you get started.
The Chinese-style tea house that you are describing (where people gather to chat, meet for first dates, socialize after a play or movie, and of course, enjoy tea and snacks) is a
very viable idea. Its success depends at least as much (probably more) on creating the right atmosphere in the right location for the potential market as it does on having expertise in teas.
What market are you trying to reach (people, demographic)? Where are those people, and where would your business need to be located (city, neighborhood/locale) to serve them? Is that area saturated with competing businesses already, or wide open? How would your new business reach this market and draw customers? What would those people expect from your business in terms of products you offer, the service you provide, atmosphere, operating hours, etc.? What type of enterprise would be necessary to satisfy these expectations? What problems might establishing, opening, and running this enterprise create for you, and how would you solve those problems?
If you can answer some of those questions, by all mean do so here -- and I'm sure that many in this community will have input to help you move forward. If you can't answer those questions yet, don't worry -- it's a starting place for your business plan. Tea houses have actually been a very popular type of business to start-up in the U.S. over the past four or five years, so there should be ample resources and experience out there to draw on as you proceed.
Hope this helps. Best wishes.