-figure at least an inch for bezel. side by side they would take up 58". if you angled them towards center then this number would decrease. the bases themselves are likely at least a few inches less in width than the screen.
- 1920x1080 is 16:9 ratio and 1920x1200 is 16:10. personal preference dictates what you buy here. personally i like the old 4:3 ratio but i've gotten used to 16:9.
-you mean led backlit versus ccfl backlit. cheap monitors with led backlighting often have a blue-ish hue to them but can be adjusted so it does not appear as bad. this type of backlighting also saves power over ccfl. in terms of image quality... there is no difference as of yet. some televisions with a grid based led backlighting design can improve contrast due to zone dimming but i dont believe any computer monitors take advantage of this yet.
-by this i am thinking you mean having both panels in either horizontal or vertical positions. 3840x1080 ultra wide ratio or 2160x1920 wide ratio. if you plan on spanning the window across both displays i wouldnt go more than widescreen unless flying a flight sim or other such program.
if you play fps games you will want either 1 display or 3 displays so the crosshair is not split.
you need to figure out what panel type you want as well.
you might also want to look into a 30" 2560x1600 display instead. it has pros and cons compared with multimonitor.
remember, the higher your resolution gets the more processing power you will need to use them.