I suggest taking all photos in color and convert to grayscale as desired in post-processing (and keep the color file handy aftrward), because you may otherwise miss out on a great color opportunity. Sure, it’ll take up more space on your memory card, but not much more, and once the photo is converted to grayscale/black and white, it’s practically impossible to re-colorize it correctly.
Besides, you’d be surprised what color can sometimes do! Would you want a black-and-white version of this?
As for your photos, some of them were good, and some weren’t. Either those fireworks weren’t too good, or you need to slow down your shutter speed to get more fireworks in in some cases. Zooming out can often help with fitting in fireworks, and remember to shoot at f/5.6 on the Av setting if you’re using the kit lens.
I’ll tell you though, fireworks are probably the most difficult things to photograph, because their behavior is wildly unpredictable. I probably couldn’t have done better than you.