Trust me... you will appreciate f1.8 vs 2.8 much more then any zoom - though I do wish there was a 1.8 zoom. You really don't need a zoom - Basketball has a very defined are where the action happens, and if for some reason action does fall outside of that area, you have both a cleaner image because it is a prime, and you have the extra stops, which means that you have the option of shooting at a lower ISO, so croping is still an option. With a 2.8, you have ISO pegged, and because of the resulting noise, your post options are significantly reduced.
Specifically, to your lens, it is pretty good but not the best. You should be able to get some reasonably good images with it though. Just remember that if you are shooting directly below the net and shooting action 10 feet infront of you, your DOF will be really thin. Cheers and good luck with it.