To be honest, did the Google Search and used the first link found back to Moodle - been some time since I visited that page ... and you are correct ... it no longer applies to version 3.5 ... and definetly not a 1,2,3 step any longer.

So let that be something of which to be aware .... documentation for just about anything can be out of date in a short time frame.  (now before some else informs it's a wiki and that anyone can change it ... I know that!).

So .... 1. yes.

2. html block or custom menus ... it's fine to show them all the time in your Moodle as they would all require login to Google to actually use them.   Did you take a gander at example provided?

Don't think you'll achieve total integration and replace Google Classroom with a Moodle that's using Google Oauth2 for authentication and Google Drive.   There's much more to Google Classroom than meets the eye.

Now the questions about Hangouts or Skype ... there used to be a plugin for Skype in Moodle, but don't think it's been kept up to date (ie, no longer compatible with 3.5) ... Hangouts ... no plugin for it.   Skype isn't Google ... so keep your focus ... don't jabber walk too much.

As far as a Hangouts block in Moodle like one sees in the interface for GMail ... not sure one exist ... probably not ... don't think you'll see one developed for Moodle either.

You might, however, be able to figure out how to use an HTML block to launch a Hangout, however.

Strongly suggest you setup a true server based 3.5 Moodle site and **begin exploring** after you get that site using Google Oauth2 for auth and Google Drive configured and running as a repository in Moodle.

Then step through all the Assignments/Activities modules provided in Moodle to see how you would use them with Google.

'spirit of sharing', Ken