There are many books about case study research methods, although nothing has really much advanced on Robert Yin's work from nearly 40 years ago. I commend his work to your attention.
Like any research project, a case study needs to start with a good research question - that is, why are you expending time and energy and resources on this study? What do you think you're going to learn? The advantage of a case study is that you have an opportunity to revise and even replace your research question in real time while you're engaged in the study, and adjust your data gathering and interpreting accordingly. With survey methods, you're pretty much stuck with what you define in advance. With a case study, your focus is on the case, on all the elements that make it into a coherent story, and you can continually adjust your focus as you proceed.
Like any research situation, it's important to bound your case study within some limits. Everything is potentially connected to everything else, and you can't possibly attend to all possible connections. Keep thinking about why you're doing the study, and what you hope that this particular case will tell you.
My own dissertation many thousands of years ago was a comparative case study of seven different instances of the implementation of a similar computer technology. My model suggested that some features of the implementation process would be consistent, and that how they were resolved would critically effect the consequences of the technology for the organization. By concentrating on the implementation dynamics and identifying parallel features across instances, i was able to show a high degree of consistency between the actual situations and what my model would have predicted.
In a later study (available on this site), my colleague Lynne Marcus and I used case study methods to look at how technology was being used in seven different adult literacy programs being implemented in various parts of the country. By gathering a lot of information through intensive conversations with lots of people in these communities, we were able to identify certain kinds of ideas and approaches that seemed to be consistently successful and others that seemed to impede receiving full value from the technology. We wrote this up in the form of a synthesis of these findings, drawing on each of the case studies as source material to support our analysis.
In short, keep your focus and modify your data gathering if you find it slipping away from you. There is lots of good advice out there on specific tools and techniques if you need it. Good luck with your research!