You are on a slippery slope, my friend. There is no limit to the amount of money you can spend on lenses, and only you can determine what are your needs and how much any given lens is worth to you. In answer to you specific questions; a prime len is a sinlge focal length, and therefore not a zoom. Primes are almost always optically superior to zooms, and can also be a stop or two 'faster'. Regarding the value of a 'fast' lens, yes you can always slow down the shutter to make up for low light, but in a sports situation you won't be able to freeze the action. In Nikon terminology, an AFS lens has the focus motor in the lens, which almost always means that the autofocus will focus faster than a non-AFS lens, and an AFS lens will usually be more costly than a non-AFS lens.
Now, more about the slippery slope. Here you need to be honest with yourself about your tendencies. If you have an appreciation for having 'the best' stuff in life, and/or if you can spot extremely small differences in photographs and those small differences matter to you, go for the best lenses now and save yourself money in the long run. What you don't want to do is to go for the 'value' lenses now, like say a 28-105 Nikkor, only to find that you start discovering its limitations later. Then you need to sell it, usually at a loss, and get a better lens which has had a price increase since the last time you checked. Wash, rinse, repeat. You will find dozens if not hundreds of posts here from people who continually buy and sell and buy and sell and eventually end up with what they should have gotten in the first place. I know, I did that too, then I learned. So, you need to know yourself to make the correct choices for you. Take some time to ponder this.
Most of all, have fun.
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-Mark