I offer you an idea that I have already used something like this.
I wanted to know the sites that my plugin uses, I created a cron job allow me to send me an email every week :
add_action('init', function() {
$time = wp_next_scheduled('dro_cron_hook');
wp_unschedule_event($time, 'dro_cron_hook');
if (!wp_next_scheduled('dro_cron_hook')) {
wp_schedule_event(time(), 'everyweek', 'dro_cron_hook');
}
});
add_filter('cron_schedules', function($schedules) {
$schedules['everyweek'] = array(
'interval' => 604800
);
return $schedules;
});
add_action('dro_cron_hook', function() {
// Here you can send the email using wp_mail() and some additional data
});