To begin the literature review you may want to read an article and make a sheet with the citation at the top and a bullet point list of important facts from the article. Read everything you can about proforma financial statements. Make a sheet for each article. (I would like a copy of the sheets also.) Then you can take the sheets and organize the important fact by topic. You can decide what is important and should be put in the paper and what is not.
Now my thought on the research question. I was curious how a particular industry is utilizing proformas. I think you need to pick an industry (for example clothing retailers, software companies, internet companies, department stores, manufactures, etc). Then for say the 30 largest publicly traded company (I would stick with US publicly traded companies because I know we can get their financials), I want you to examine what types of items are they putting in the proforma. I want you to find at least 30 companies in that industry who use proforma. I want to see if there is a trend of what they are doing in the proforma. But of course before we can start this the literature review needs to be done to see what is already discovered on the topic. You may find a project like this done for one industry. We can extend the literature by doing it for a different industry.