Setting up Google Tag Manager / Google Analytics with Commerce7.

Today Commerce7 is fully integrated with GTM which can be used to connect with GA. 
To set it up - in WordPress you will need to add the GTM containers to the head and body tags.
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 - 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.