I wouldn't worry to much about waiting to get a case, I always tend to get that and the motherboard farily soon so i can start to get a vision. saving the graphic card then the CPU for last since they are the 2 most expensive, and fast changing.
4 gigs is excessive i believe. A game like fear uses just over 1 gig. a I'd stick to 2gigs for now, and when need be, upgrade to 4, i doubt even Unreal tournament will use 4, much less 3.
Also, instead of getting an All In Wonder video card you might look at getting the ATI pci video tuner card instead, that way you keep that card for your next upgrade, thus saving you money on your next purchase for a video card. It only cost 80 bucks i believe.
Agiea is coming out with its physic cards soon also. I wouldn't reccoment getting one just yet, Id wait to see if its worth it with benchmarks. But its something to watch.