I'd bet most people on MFK fall into the "knowledgeable" category at most, even if they don't realize it. An "expert" to me is someone who would likely have formal education in ichthyology and extensive knowledge with the hobby and a master would be someone on the level of a PhD that has studied species in their natural environment. A master in training would be moving towards these goals.
If you don't have formal education on the subject, you ultimately are just a hobbyist. You may be a very very knowledgable hobbyist, but you will likely never fully understand the many aspects of the chemistry and biology of the subject.
As far as keeping "a few exotic fish," anyone with the money can go buy any fish they want.