The task you have is a similar one posed to many undergraduate students in compiler courses every year in thousands of universities, and the notes you cite are good sample of the many sets of course notes available on the topic.
The solution is the same as any software engineering problem: testing against the specification.
Although the intellectual problem of the analysis and creation of AFDs for a whole language by hand might seem overwhelming error prone, don't forget you are tasked with also implementing this (in your chosen language of Ruby).
This implementation can be tested by feeding it carefully graded and selected samples of C language input. When it does not deliver the expected result there error will either be in the coding of the AFD or a fault in the AFD you constructed. You make the necessary change and go around the testing loop again.
You will eventually end up with a valid AFD for the entire C language and an analyser for it written in Ruby.
It is often a good idea to start small and implement a subset of the C language and get that working first and then add more to it using stepwise refinement. This is a less risky strategy than attempting to do the whole thing in one go.
You need to apply all those techniques you should have learned about building specifications, designs, programs and testing and apply it to this problem. Just apply good computer science and software engineering to this problem.
