I'm not sure what you are asking. You've just named a couple of good primary sources: Thucydides and Xenophon (Plutarch no so much). For the democracy and especially for the end of the 5th century, the comic playwright Aristophanes is a great source, especially Knights, Acharnians, Wasps, and Birds. For the Persian Wars, Herodotous. There is also Pseudo-Aristotle Athenaion Politeia, or "Constitution of the Athenians." We also have a huge library of epigraphic sources for Athens in the 5th century. There are various volumes (like Meiggs and Lewis) which collect the most famous for ease of use.

For insights into Athenian culture, some other Aristophanes plays work well, like Lysistrata, Frogs, Thesmophoriadzusai, Clouds, or Peace. There are also the three great tragedians Aeschylos, Sophocles, and Euripides, all of whom lived and wrote plays during the 5th century. Also, the dialogues of Plato. Edit: also, a huge wealth of artistic data: painted fineware pottery; sculpture; the art and architecture of the Athenian acropolis, including the temple of Nike, temple of Athena Parthenos with its famous metopes and frieze, the Erechtheion, the Propylaia, etc etc.

Plutarch is fine if you are just looking for basics, though keep in mind that he was writing half a millennium later.

I would also recommend Perseus Digital Library for free and easy access to ancient primary sources.