Well, IMO I would stick with the slim mini-ITX design to keep it small and compact. But those parts would work fine. I would actually try this: http://www.newegg.com/Product/Product.aspx?Item=N82E16819103886
You can unlock the 4th core and have an athlon II X4 for the price of an X3. Don't overclock it though, but the unlocked core should be great. This processor would even be fine to finish this pc AS a media center PC as well. So, maybe you'd have this as your NAS for temporary, and when your budget is restored you can go for a full build on a dedicated NAS PC.
edit: Taking a look at the ECS board again, it looks really good. Has a beefy VRM and it also has a nice 2 digit debug display on the bottom right (i'm planning to buy a POST card as a tool of mine, I find this kind of thing to be a necessity) Also packages a 880G chipset (being a G series, I don't trust) but it's very feature rich and can handle some light overclocking, so I take back what I said about not overclocking.Edited by jtc10512 - 9/6/12 at 2:15pm