Setting up Google Tag Manager / Google Analytics with Commerce7.

Today Commerce7 is fully integrated with GTM which can be used to connect with GA. 
 
Setup:
To set it up - in WordPress you will need to add the GTM containers to the head and body tags.  https://developers.google.com/tag-manager/quickstart
We felt doing this in WordPress would give you the most control.
There is nothing to configure on Commerce7.
 
Enhanced Ecommerce:
We implemented the Enhanced Ecommerce from https://developers.google.com/tag-manager/enhanced-ecommerce - and we did it on the window.dataLayer (as opposed to a custom data layer).  
We followed this documentation explicitly except that we didn't implement refunds and promotion impressions.  You will get product impressions, clicks, checkout steps, etc.