Vista 64 is fine, however if you plan on buying it (meaning you don't already have a copy of Vista 64) then I'd recommend using the Windows 7 beta, and then when Windows 7 comes out you can just pay and get a copy of it...
Seeing as you want to go with Vista/Windows 7 environment, and want support for that many hard drives, (and I'm assuming you want some fault tolerance) your going to have to go with a hardware raid card. I haven't kept on top of that lately for media servers, you might want to pop over to the media server thread and read the last 20 to 30 pages of it. Once you do that, and if you still have questions, feel free to post.
Personally, I feel fiber optics is way too expensive for personal use now, I'd run a few lengths of cat 6 if your doing a new install. This should give you plenty of bandwidth for the foreseeable future. Especially if you use a non blocking switch/router as a central transfer point. For home use I'm a big fan of go with what you have or can do easily, and only upgrade if that no longer meets your needs.