Nginx best high performance caching configuration for WordPress

I am planning to deploy an optimized LEMP stack on DigitalOcean on Ubuntu 18.04 for my WordPress site. I have many question and confusion related to caching. I hope I will get all my answer here.

1. Are PHP-FPM and Varnish technology the same. Which one should I go for, Varnish or PHP-FPM for my Nginx server?

2. According to my research, a combination of Redis and PHP-FPM gives best performance. Is this right or should I go for radis+varnish?

3. As I know, Redis cache database query. So, if Redis only cache database then how PHP-FPM/Varnish works together with Redis to produce the web page very fast?

4. As I know Nginx can’t process PHP request, so by default PHP-FPM comes here to serve the PHP request, Right? If right then PHP-FPM should already be configured in all the server set up. Am I right? I am using all the DIGITALOCEAN tutorials to set-up my server.

5. After all the above set-up, do I need to use any caching plugin on top of my website?, e.g., WP-rocket or Swift Pro.

6. A caching plugin also generates static HTML pages of a website and saves it on the server as PHP-FPM or Varnish do. So why we should use both caching plugin and server-level cache?

7. Without installing a caching plugin, will my website give browser cache facility with the above set-up? Or it is necessary to use plugin to get the browser caching facility.

If you have more recommendation then please guide me. Thank you!