1. 23-24" Full HD instead of 22"
2. Just the one HD 5850
3. Asrock 880GExtreme3 every bit as good as its 890GX cousin cept with slightly inferior IGP (irrelevant in your case)
4. I would pick either of these casings
a. NZXT Hades
b. Cooler Master 922
either has great cooling and fits longish GPUs like Hemlock HD 5970
5. Tight budget and if apps not memory intensive 4GB DDR3 is fine for mainly gaming rig