Dear Chun,
I forgot to this point, when you pose as a mysterious customer in a competitor's shop, you need to find out how much each customer spend, we call it basket (as in a shopping) count.
You need to know as much information as possible in the location where you are going to have your business in order to establish whether it is viable to invest your money into that business.
All these information is required to put on the business plan and the figures will then tell you whether it is a viable business or not.
I think it will be clearer as I talk you through these stages of setting up your business.
Ian