Hello,
Kindly note that we are team of experts in Magento working since 2010. We have been working on numerious projects, extension development, theme integration etc.
We are specialized in magento and ready to start work asap.
We will fix your 500 error issue for which we need complete access of cpanel, ftp and admin panel. Also, Varnish tarpentine is just an installation of Magento extension provided by nexcess hosting provider.
Please confirm if this is the job request.
Regards,
Sankhala Info Solutions