I taught business classes at a university and encouraged my students to use the library rather than just rely on the internet for information. Much of the information you are looking for is not available for free and libraries subscribe to data bases that you as a student or patron can access. Start with the reference librarian in the research department of the library.
Secondly, every business type has a number. These numbers would be available in the reference part of the library. They are multidigit numbers that hone down the exact type of business. For example clothing stores would be differentiated as to whether they were men's, women's, children's, sporting etc. It is often helpful to have this number so when you do further research you will know you are in the right place.
Another comment above was also insightful in asking is this a brick and mortar or online or a combination? This would greatly alter your plan.
The Small Business Administration website also has a wealth of information.
I don't know the extent of your assignment. Generally, in an into to business class it is to get a feel of what is involved and most business plans written for these assignments are not as extensive as one would be to actually start a business. If you are unsure as to how far you need to go on this assignment talk to your professor. For example, do they expect financials, cash flow, staffing, renovation budget, market research (competitors, population data) etc which would be part of a business plan presented to a bank or investors. My hunch is they don't want something that extensive but you had better find out.
Good luck!