Thanks for keeping me honest, but I don't have the book available to me now either. If you can quote from a different language edition (especially German), that would help.

Without the book to review, what I relied on in my comment[^1] was this: When I first read it, I came away with the impression that there was no secret. I remember reading about Petunia's letter and concluding that the Evanses knew all about Witches and Wizards. (The differing reactions to them are like the attitudes towards Mutants in Marvel comics.)

[^1]: That, and checking the Wikia for first mentions.

Perhaps, primed by this, I missed later references to secrecy. (But that doesn't help with any comments by McGonagall in the prologue.) I do remember being disappointed (but understanding) with the secrecy in book 2.

Regarding Azkaban: No mention in book 1, yes, but it is mentioned in book 2, before it started to play a major role in book 3.

Yes, certainly. In fact, I always thought that Hagrid's trip to Azkaban in book 2 was set up so that we'd know what the title of book 3 meant. (I knew that title before I read book 2.)