I like your enthusiasm. One of the great things about running Linux on a home server is it can fit well withing any budget you have. I just transitioned away from Ubuntu, which is what I did the vast majority of my early learning on, so I would recommend that. Very easy to get a good, solid server up and running while still learning a lot in the process. I will forewarn you, though. The learning curve of *nix is very, very steep if you have an all Windows background. However, with that said, I'll be more than happy to help where I can. Just gotta keep an open mind and keep moving forward.
The hardware you have listed should be more than adequate for a personal server (depending on the use). Which brings me to my next question: what are you going to be using this server for? File Server? Proxy/Cache? HTPC? Once we determine the uses for it, it will be much easier to recommend more specific software packages and tools.