Wow, I wrote a really nice answer last night that apparently didn't go through... let's see if I can remember it...
If you have Netflix, check out Episode 2 of Greeks: Crucible of Civilization. It's a PBS produced documentary and is narrated by Liam Neeson. Episode 2 has some good information about how their navy formed, how to helped them by way of military and trading, becoming a world power, etc. This will also give you another source of information. You don't usually see tv programs as sources, and it's always good to see something other than book and especially internet sources.
Try separating the first question and expand.
Why did they have such a large navy? What percentage of the population was in the navy? What would those numbers be like in today's population? Compare their navy to a navy of today?
How did the navy impact their society? Military? Trade? World power?
Could anyone join the navy? Were people drafted? Were slaves made to join? What if their masters joined/were slaves expected to join or did they just have to go or were they allowed to stay home and attend to the matters at home? Were certain classes/families expected to join?
What is the history of the Athenian navy? Why/when did it form?
What were their ships & technology like? Could they withstand strong storms? What were their docks/ports/bridges like? What was the ocean around Athens like? Was it prone to storms or fairly relaxed?
Hope this helps and good luck! I love projects like this!