Google Tag Manager has hidden super powers when mixed with a bit of jQuery & javascript allows us to do (most of) the tracking directly within its interface.
If you are missing transactions and sales from paypal in google analytics ecommerce tracking. This post will help explain why and possible ideas to fix it.
Step by step instructions for adding multiple Google Analytics tracking code on the same web page without interrupting the reports. Included the scripts
Google Analytics is not just a traffic reporting tool but a centralized hub for all marketing & sales data. See where GA is heading and some ideas to benefit from.