The research process is just that: a process. A good researcher isn't someone that puts the right words in the search box the first time, it's someone who uses each search to improve the next one. By being aware that you'll circle back and perform tasks more than once, use more than one tool, and look at more resources than you actually use, you'll be better equipped to plan how long your research takes and pick the best sources.
As you work through your annotated bibliography and your review of literature, you will need to narrow your focus to figure out the specific issues and questions that you are interested in!
One techniques for getting started with research is to create a concept map to work through your ideas. Creating a concept map, with your broad topic in the center, can help you focus your topic and come up with keywords to use in your searches.