Do I need caching plugins in addition to the 20i CDN?
The short answer is no, the 20i Content Delivery Network takes care of caching for you. The free 20iCDN caches static content and stores it until it's purged via the Edge Caching section in My20i.
This means you shouldn’t use any additional caching plugins such as W3 Total Cache or WP Super Cache.
Therefore, you don’t need plugins such as WP Smush, Lazy Loading, EWWW Image Optimizer or Autoptimise.