(...)
Since MPM is turned off by default in httpd.conf
No. It's enabled the module "mpm_event".
Check with:
# /usr/local/apache/bin/apachectl -M | grep -i mpm
(...)
Current setup is Nginx -> Apache -> PHP-FPM 7.xx
Besides Apache settings should i change any other settings to better utilize the resources?
Thanks in advance
The MPM Event is needed to run PHP-FPM.
You can choose another MPM just with PHP-CGI.
It is a Apache module/PHP limitation.
Surely, PHP-FPM have a superior performance, included with Nginx<->Varnish<->Apache, but you can have different problems with greedy caching with Varnish.
Your choice.