Dear friend,
I have read your requirement carefully, I can help you check and fix your site and make it more stable, fast and secure. I will check your mysql, nginx/apache, php, varnish config to find problems and optimize them. I will also check your extensions and php source code to find the bad code and optimize.
Please contact me, I will start immediately. I will be more than happy to do this job and build relationship with you.
Regards,
Jimmy