Speedup and Optimize two Wordpress Onlineshops on a Debian 8.8 Apache dedicated Server

We have two mostly similar Onlineshops (Wordpress 4.8.2 and WooCommerce on a Debian 8.8 Server and Apache under PLESK) running one for .de and one for .com domain. Both online shops are separate installations. We need a professional web admin to perform some server side and Wordpress optimizations to achieve better Google PageSpeed Insights ratings and to optimize page performance (main and all sub pages, both domains). Tasks: 1). Currently our PageSpeed Insights rating is Mobile 54/100 and Desktop 64/100. We want to achieve around 95 to 100 points. This task includes possible image optimizations (as far as possible without significant quality losses), server side optimizations (memcached ?, varnish ?, configuration ?), Wordpress side optimization (caching, if possible without compatibility problems). 2). Check both Wordpress and Server for further speed optimizations, if not done in first task. The tasks have to be completed till Sunday evening GMT+1 time as both pages are live and we have a lots of customers during the week days. Also the project includes the optimization of both installations .de and .com