I think you need to start with a plan. What do you want to use your log files for, what rules do you plan implement on your logging system, how do you plan to audit your logs, what do you plan to audit your logs for, what operational rules do you plan to put into place with regard to log management, and ultimately what is the problem you are trying to solve by implementing a log management system in the first place. Once you begin to answer these types of questions you can begin to formulate a plan and decide what logs you actually need.
I just read an very interesting blog on how Etsy is handling something very similar (thought not exactly the same); I found it very interesting so if interested you can read that HERE.