Apache and PHP possibilities, now we have FPM

Now with Sympl 12 we have the option of PHP-FPM, I am thinking of the possibilities for performance improvement and reduction of memory usage. My knowledge of Apache configuration is fairly basic.
I now have one or two sites using PHP-FPM, and many using the default mod-php. Apache is still using mpm-prefork as it seems to be required for mod-php.
Questions for Apache experts:

  • If I convert most of them to PHP-FPM, does that mean I could reduce the number of apache processes, as fewer will be needed? (as I understand it, this would only apply to PHP files; other files like CSS, text and graphics would still be handled by an apache process)
  • If I convert all sites to PHP-FPM, would I be able to disable MOD-PHP altogether, making each apache process smaller?
  • If I could do that, would I then be able to switch to mpm_worker or mpm_event, or would that break Sympl?
  • What improvements in performance or memory use could I expect from any of the above steps?

I’ve read lots of general online advice about how to run PHP with Apache and the different MPM options; my main concern here is compatibillity with Sympl.