At lower f numbers you can have a greater depth of field, allowing the main subject of the image to be perfectly in focus, with the background nicely softened. The photographic term for it is bokeh (
https://en.wikipedia.org/wiki/Bokeh).
A lower f number is a wider aperture, which lets more light in, allowing you to take photos even in lower light situations.
Just as an example, in the past with my D3200 and both the 18-55mm Kit lens, and also a Nikon 55-200mm, when shooting motorsport, the lenses struggle to even focus as soon as it becomes overcast, or towards the end of the day as it starts to get dark.
By contrast at my Niece's wedding recently, my Nikon 50mm F1.8 was able to shoot indoor shots in relative darkness during a Disco, without even using the flash.
As long as you are buying good quality branded cards like SanDisk, Lexar, Samsung etc. then failure should be fairly rare anyway.
I personally would buy several smaller cards, even say 4x 16GB cards, as 16GB still holds 300+ photos (at least on my D3200), as you then you can always have an empty card on the go (i.e. don't have to clear it between shoots, and don't have to risk losing any already shot photos e.g. if your camera is stolen with a single big card in it.)
