I've done the exact same, only using Debian instead of FreeBSD. I have an old K6-2 with 256 MB RAM sitting in the computer room, doing web serving, FTP, SSH, backup...anything you can think of, it probably does it (flawlessly, I might add).
What I would suggest is first, if you've never touched FreeBSD or any other hands-on UNIX system before, is to read at least some of
this article and links. Once you've gotten a firm grasp on FreeBSD (or whatever you choose in the end), move on to more FAQs and articles, perhaps
Apache's wonderful FAQ.
Reading up on as much as you can and/or want to know about will really improve your success of the initially daunting task of setting up a server. Definitely read the "Read Me" files in any package you wish to install, as they will give you helpful usage tips. They're not simply copyright information or installation instructions like some Windows or Mac Read-Me's can be.
Good luck, and have fun. You'll learn quite a bit. Post here again if you have any questions!