Instaling GameHosting

Hello i have an dedicated server with 32 IP Adresses , and i install virtualmin + webmin , and now i want to make a game hosting ,I want to give a client a username and password to manage Counter-Strike server, install various plug-ins and access to some files inside server Counter-Strike, from what I understand all this stuff is made of modules. how i can give acces only for then server

you would create a virtual server (domain) even if the name is made up and let them login over the resolvable name (server name).
Each domain would need to have its own gamefiles (CSS Server) though, so you would have multiple installations

If you have the resources I think it is better to create a VPS for each gameserver. Thats what I do.