when does Odysseus reveal his identity? how has he been careful in keeping that information to himself from Books 5-8?

Answer 1

Odysseus's men knew who he was, but then eventually, he lost all his ships and all his men over a period of time through many dangerous adventures.

If you're referring to when he revealed his identity once he got back home, look at books 23 and 24.
http://www.sparknotes.com/lit/odyssey/