Obviously I know the more fantastical things aren't real like cyclops, Atlantis and super powered aliens.
What I mean is the conflict itself and the interactions of the city states. I'll simplify with direct questions :
How common was naval combat? Are the ships in game historically accurate?
Were there really mercenaries and bandits just...everywhere?
How accurate is the weaponry?
How large were the battles? I'm thinking it is a limitation of the system but conquest battles are like...150 dudes tops.
Was everyone just having sex with everyone? (Alkibiades I'm looking at you here.)
Sokrates, Perikles, Kleon, Brasidas, Pausanias, Archidamos, - all portrayed correctly? Did Sokrates help Perikles and overthrow Kleon? (I know Kleon and Brasidas died in the battle of Amphipolis - I googled that much at least)
Oracles, Pythia and fortune tellers: were they all so trusted that they literally threw children from cliffs over their word?
Speaking of Pythia, was it really the Spartan Pythia who stopped Leonidas from rallying a larger army against the Persians at Thermopylai?
What was the truce of Olympia Valley about?
Were the Olympics really so small back then? It looks like a 45 minute affair as an excuse to drink all night rather than a big sporting event but they seem to put a ton of importance on who won. Why?
Herodotus: did he really just travel the world with random people? More importantly though, is there any evidence of a lost work written by him?
I'm not sure I can respond in a substantial or contributory way because I'm seeking knowledge without much to add to it but I thank anyone who takes the time to answer even one of these questions for me.
Hi! I actually did an AMA about this around the time the game came out, which answers most of your questions. For another perspective there's also the series of articles on AC:Odyssey by archaeologist Dr Josho Brouwers at Ancient World Magazine.
Just to touch on some of your specific questions:
Were there really mercenaries and bandits just...everywhere?
The game has a pretty weird way of "gameifying" mercenary service, where you can just rock up to a commander and join an army even as the battle is about to start. In reality, mercenary service in Ancient Greece didn't work that way. Mercenaries tended to be hired as a group, with heavy infantry usually organised into groups of about 100 men under a commanding officer. This would be done well in advance, during the planning stage of a campaign, not on the fly. Therefore, if you were looking to get hired, you'd head for one of the places where mercenaries were commonly found (in the Hellenistic period, the particular hotspot was Cape Tainaron in the Peloponnese) and wait for an employer to show up.
How large were the battles? I'm thinking it is a limitation of the system but conquest battles are like...150 dudes tops.
This is clearly guided by the limitations of rendering each individual warrior's actions. In reality, a small Greek battle between local states might involve only a few hundred men on each side, but the battles of the Peloponnesian War saw large states and coalitions field armies of many thousands. At the start of the war, Athens had a field army of 14,000 hoplites and 1,200 cavalry. In the largest coalition battles of the Classical period, such as the Nemea in 394 BC, there could be as many as 60,000 men on the battlefield.
Did Sokrates help Perikles and overthrow Kleon?
The game took historical figures and rewrote their storylines. This is fine as far as creative license goes, but of course it's not history. As you said, Kleon and Brasidas both died at Amphipolis in 422 BC. But Perikles died of the plague seven years earlier. Sokrates did not have a political role in these events, though he did serve as a hoplite at Amphipolis.
was it really the Spartan Pythia who stopped Leonidas from rallying a larger army against the Persians at Thermopylai?
The Pythia was the name of the priestess of Apollo at Delphi who acted as the voice of the god. After the defeat of the token Spartan force at Thermopylai, the Spartans spread the story that they had only sent such a hopelessly small army because the Pythia had told them that a Spartan king had to die for the rest of the state to be saved. Since the army was on a deliberate suicide mission it made no sense to send more. We can believe this story if we like, but there are other explanations, which I go into here.
What was the truce of Olympia Valley about?
I'm guessing this is a reference to the Olympic Truce. The Greeks recognised a few temporary general truces (literally "hands-off") which served the purpose of allowing everyone to participate in major Games even if they were formally at war with other Greek states. There were four games for which a sacred truce was observed (the Nemean, Isthmian, Delphic and Olympic Games). All travellers to and from the games were considered to be under divine protection and to harm them would incur the wrath of the gods. Even in Antiquity the games were a major event that would go on for days, with different contests and many participants from all over the Greek world.
Herodotus: did he really just travel the world with random people? More importantly though, is there any evidence of a lost work written by him?
Herodotos does seem to have been well travelled. As a young man, he was exiled from his native Halikarnassos, and spent the rest of his life travelling around the Eastern Mediterranean and parts of the Persian Empire, helping to found a city in Southern Italy before eventually settling down in Athens. The work we have of him, which survives in full, is the only work of Herodotos that anyone knows about. Often other ancient authors can tell us about other works that are now lost, but no one ever suggests that Herodotos wrote more than one.
Happy to help if you have further questions!