For visual configuration purpose i would take a look at the tinymce advanced plugin. and about the font example you’ve asked for i would try something like that (untested)
function tweek_mce( $init ) {
$init['fontsize_formats'] = "8pt 10pt 12pt 14pt 18pt 24pt 36pt";
return $init;
}
add_filter('tiny_mce_before_init', 'tweek_mce');
place it inside the functions.php. no acf needed in that particular case. best regards ralf