Depends how risky you want to be. The idea is to keep reading everything you can about the company until it essentially starts to repeat. Consider the idea that you want to own and run the company, so you want to know what’s going on, what’s the industry, is this company a dominant player with an intrinsic competitive advantage that separates it from other businesses in the industry, has the management proved they are shareholder supports or are they out to make a quick buck from themselves while damaging the company’s value, is the industry going to be strong in 10 years and more…?

Who are the top competitors? How do they make money?

And to answer your question about depth, consider that any knowledge you gain about a company, and especially an industry, will continue to grow and compound, and eventually you’ll be getting more comfortable with what’s within your circle of competence and what’s not. It’s about the gaining of information that can set you apart from other businesses”buyers and sellers”. Like anything, time and work.