I'm looking for an answer as to how to know the source files that I need to mention in the Makefile if I'm writing my program from scratch. Are there some bare essentials? If so where can I find the resources to know them?

Apparently there is some limitation on length of the paths with Keil. The paths are specified under "Options for Target" --> C/C++ --> "Include Paths". Due to this limitation paths look like this: ..;..\..\..\..\..\include;..\..\..\..\..\include\app_common;…