The acadamies will only teach you basic stuff (deff needed), but they will take you only so far.
I'd start with the free tutorials these guys give, and then potentially go from there: analyticsmania and julian gtm (just google him like that).
Then, the god of them all: Simo Ahava himself. You won't go wrong following these 3 (just make sure you're following an updated article).
GTM groups on FB/Slack are also a good place to start. Slack group is called: meassure.slack.com (I think founded by Simo himself)
Good luck!