Ferraris are awesome but you're unlikely to sell many where I live. We will hold regular events with professional cyclists, like demonstrations and autograph signings, to bring more customers to the store as well as to extend the athletes' "brand" to our brand.
How much? Information about your market must be detailed in your business plan, and you must show great awareness of your opportunities and threats, which requires considering your strengths and weaknesses. Online retailers will also provide competition, but thoroughly analyzing those companies will be less valuable unless you also decide you want to sell office supplies online.
Every business has competition. What is the size of your intended market? While most of the information you find will be anecdotal and based on the opinion of just a few people, you may at least get a sense of how some consumers perceive your competition. If that's the case, provide detail on segmentation that supports your plan.
That's why marketing plans and strategies are critical to business success.