1. Yes, if it's 3 x 1080p.
2. Hardly, don't expect playing on high settings.
3. It would work better than the GTX 760, still nowhere close to maxing out games.
4. Maybe with low setting in old games.
5. Eyefinity: http://www.tweaktown.com/tweakipedia/8/how-to-setup-and-configure-amd-eyefinity-multi-display-technology/index.html
Nvidia surround: http://www.cclonline.com/article/1193/Guide/Graphics-Cards/Configuring-Multiple-Monitors-NVIDIA-Surround-Single-GPU-/
6. No, I'd recommend using only high end (a.k.a expensive) cards, since you couldn't play on high or even medium settings with fluid fps if you spent 300$.