Anti-aliasing. It's extra sampling to smooth out jagged edges. It can make the picture look better but it causes a performance hit and uses more VRAM.
You won't need any aftermarket fans with that setup.
It will last a while for 1080p 60Hz gaming.
120Hz is actually very hard to do, not for graphics cards, but for CPUs. At that refresh rate, CPU becomes a huge bottleneck as it stuggles with the game engine. For the graphics part, you can always get a faster graphics card or turn down the settings to get 120Hz, but if your CPU stutters it won't make a difference. This is why I tell people to get higher resolution instead of higher refresh rate.