Expert in Wordpress Multisites server setup & Management

We are looking for an EXPERT in WORDPRESS MULTISITE SERVER SET UP AND MANAGEMENT to provide a solution for Wordpress Multisites Hosting aimed at Millions of Clients Like How WORDPRESS DOT COM Works. We are Using One Single Root Domain (One Single Cpanel) to Host ALL the Subdomains, so Clients Have No Access to Cpanel of their Own, But they Only Have Access to WP Admin to Edit Or Customise their Websites/Blogs. We also Provide a Full Domain to Clients which We Map in the Cpanel to Replace the Subdomains. The Set-Up We Have Creates Subdomains in Cpanel then We Map a Full Domain to the Subdomain. We already have an Existing Dedicated Server Hosting 6,500 Client Accounts and We Aim to Grow to Millions of Clients. The Sever Has been slowing down when accessed by a substantial number of users, to an extent of timing out. The database has been unstable in that even though the database server is up and running still a user gets databse connection error. My Server is at Hetzner is that the best location or you have reservations? My server is meant to hold over 1 million users or sites but it has the following specs (Centos 7, 256GB RAM, 24TB storage, MariaDB, Litespeed, Cloud Linux) will this suffice? MySQL server goes down often Wp_admin times on adding of sites manually by the admins how will you handle that? WP_admin getts error 503 on adding users and sites how will you remedy this? WP_admin login pages for individual sites being blocked by cookies how will you remedy this? On matters of resources, how do you plan to manage this now that we use addon domains and not Cpanel user accounts for the member sites? How will you address the issue regarding database cache size? +254797951388