A good RQ is researchable, and a good researcher knows to modify an RQ when enough (good) information isn't available. You can't know for sure that your RQ will work until you begin researching. You can, however, make sure that you start the research process with a well-formed RQ.
When it comes to research, you won't know what's out there until you start.
You know what you need (8 sources, 5 scholarly), and you probably have a good idea of what you want from your sources (5 scholarly sources that perfectly support your arguments, and 2 good newspaper articles, and 1 great website), but until you begin researching you won't know what's out there.
Often, the hardest part of research is finding the right words to get you what you need. You can eliminate some of these "unknown unknowns" by turning your RQ into a search strategy before you begin: