Welcome to Cloudways.
To answer your questions.
The varnish cache is installed and enabled on all the servers by default that you launch through Cloudways. In order to use Varnish caching on your website, you need to install a plugin that establishes communication between website assets and the Varnish on the server.
Breeze is our in house built plugin that is lightweight and free to use with features that are easy to setup, the issues addressed in the video like minification, grouping and exclusion are already being addressed.
If you have a highly complex and dynamic website that requires you to individually add rules for scripts , CSS, CDN etc. then it makes sense to look for a paid caching plugin like WPRocket or a free plugin like W3TC.
For anything less complex, I would recommend you to test Breeze for better compatibility with our hosting servers.