CentOS | HowtoForge - Linux Howtos and Tutorials

That is a great place to get howto articles. If you have yum then installing proftp should be as easy as yum install proftp

Here is an article that will help you setup the server: CentOS 5.1 Server Setup: LAMP, Email, DNS, FTP, ISPConfig (a.k.a. The Perfect Server) | HowtoForge - Linux Howtos and Tutorials

In order to get your domain to point to the box, setup a A record that goes to the IP address of the box. It's that easy. I've never used webmin so I don't know how or even if that handles virtual hosts so you can have multiple websites on one server.

Edit: I'd highly recommend going with a managed dedicated server since it sounds like you have no clue what you are doing. A lot can go wrong if not setup correctly.

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Eric