To become a bitcoin expert you must know everything. It's kind a hard but if you really a hard working it will be easy for you. Read books, research, etcetera. I think all knowledge that we need is in the google now so it will be easy for us. Ask from the already experts on it. I think you must talk to them too so that they can share their experience too and they can inspire you.
I don't really get when you say "bitcoin expert" since using and knowing them can easily be obtained. Also, being a "bitcoin expert" doesn't mean you must know everything, but know wholely what bitcoin is and help the developers to give some proposals for some of it's problems.