To build any expert system, the first step is to interview the expert to get a scope of their knowledge. Not to get all their knowledge, just to find out how big the topic is, what the major categories are, etc.
So your first step is to find an expert. Who do you know who is willing to donate a significant amount of time? Even if Quantum Mechanic Bio Engineering would make the perfect expert system project for you, it's not worth considering unless you have a Quantum Mechanic Bio Engineer with spare time on their hands.
So start there: Who do you know who is smart and bored?
