Plato the republic - question/theory?

First, Plato is not talking about a republic in the modern sense of the word. You are fostering this meaning on the dialog. Remember that the real question they are trying to answer is "what is justice." Socrates suggests that since a city is larger than a human being, but that justice would be the same in both, it would be wise to look for justice written large in the city. There is a discussion of types of government and democracy does not fare well. Plato has in mind the type of democracy that was being practiced in Athens. He has no idea of a representative government. Democracy is dangerous, in the dialog, because the many do not care about justice or for what is best, but only for what pleases them. Socrates builds the ideal city state giving various reasons why the artists and the poets should be shown the gates and why philosophy must be honored.