I have posted a related question in another topic in this forum. We had SSO between Moodle and Google Apps working in 2.4, but something has happened to stop the creation of new accounts using the Google User Sync block since we upgraded to 2.5.
This issue aside, the setup wasn't too bad - and the process of creating new users in Google Apps and the SSO worked really well. I basically followed the published instructions, with a few needed modifications (that I found by doing the same kind of reading that you've been doing). Fairly small changes, really. I won't bother you with details now, because, evidently, I'm doing something wrong for the 2.5 environment - and I don't want to hobble your installation! I think I've bookmarked the sites from which I got information to fix the few problems and can pass those along.
Please post your results if you move forward!
David