It's pretty simple.
--wpfc to configure your site to utilize FastCGI Cache.
- Install Redis Stack on the server,
wo stack install --redis
- Install "Redis Object Cache" plugin and activate the object caching from plugin settings.
Cloudflare increases TTFB in most of the cases as it works as a proxy between the user and origin server. Even if you use Cloudflare's Full Page Caching, it will still be slower then serving your site from the origin without CF Proxy.
Unless you're on their Enterprise plan, Cloudflare doesn't ensure the network routing from the nearest PoPs. Here in India, it serves the sites from Japan, Singapore, Pakistan etc instead of their Indian PoPs.
Using Cloudflare with Full Page Caching is worth it if you have a global audience but if you have the site audience from a particular country then I will strongly suggest using Cloudflare in DNS Only mode and serving site from origin server as long as you care about 200-300 MS difference in the load time.