First, thanks for comprehensive answer.
Thanks, I read it just now and now is clear for me.
It is actually already 'standard' for all 'top' caching plugins and it is not just how you should to include it, but also should be enabled by default.
I didn't know about it, thanks for info.
Thanks again, I get it.
I cannot to do it, as it is about startup sites and 'always free' on GCP is only possible (available) with WP at the top of LAMP (if I will use Bitnami). So, startups are low resources and traffic, will be stupid to pay when it can be free until it will not start to 'produce'.
I will post it in next reply. However, as you want to see what's going on, I will make it 'barebones' (no other themes and plugins and no server 'tweaking'. However, Let's Encrypt will be enabled.