FOV determines how much you can see. Higher is generally better, but too high will start to look odd.
AA (Anti Aliasing) is edge smoothing. This takes a big hit on performance so you shouldn't be setting it to 8x (or 16x) unless it's an old game and your framerate is in the hundreds. I find 4x is fine at 1080p (on a 22/24 inch screen), but 2x is still a lot better than none.
AF (Anisotropic Filtering) refers to texture detail at angles/distance. On modern machines this has very little performance impact so I recommend setting to maximum (normally 16x).
It depends. I myself for instance can't tell the difference when FPS goes any higher than 45. Above that every FPS seems like the same to me. Same is with AA and Ani. About the fov well the ideal fov is 90. Here's my preferred setting and any thing higher than that doesn't look different to my eyes: