Wow, there's really a lot to that question. To keep it as short as possible, you sould be able to keep the same router. You will just have to pick which device will issue DHCP addresses. The Linksys routers have the option to issue addresses or pass-through addresses, which means you would have to set up the DHCP server. Probably better to let the router do the work.
Then, you really need to brush up on some server work depending on what you mean by controlling the computers and to what level. Printers are very easy; depending on how they are connected to the network, I'm guessing through a wireless card. You just set a static IP address on the printer and create a port on the server to that IP, install a local printer on the server using that port and share it out. Then the other computers will be able to map to the \\server\share name.
For file sharing, all you need to do create a folder that all the shared files and folder structures will go in and share the folder. The computers will be able to map to the \\server\folder name. It gets more complicated if you want to restrict some user access to certain files. You will have to install the Active Directory services and create user accounts. Then you will just edit the permissions on the folders and restrict or add specific users. You can also have the users map drives to the server at logon by creating batch files and put them in the \\server\netlogon share and assigning certain users to specific batch files in Active Directory.
There's a lot to it, but I hope this gets you started.
