depends on how far/close you can get and what types of shots you are trying to get. I'd feel pretty comfortable going in with just a fast 50. It's a good in-between length on the ff, neither too tight or too loose. if i end up being limited to up close, i'd make shots of the individual members, further out and i'd do more of the entire band/venue. if you're the/an official photographer for the event, this should be a non-issue.
i wouldn't want to shoot with anything slower than a 2.8 for concerts and club type events, so imo that kit lens would be useless anyways. VR means jack sh*t when your subjects are moving around, sometimes you just need honest to goodness light collection.
if the lighting is really rapidly changing, shoot manual or your auto exposure will be jumping all over the place giving inconsistent exposures and/or widely varying shutter speeds. shoot raw, set it to some average exposure value (or for some tolerable limit of iso/shutter/aperture) and correct out any under/over images in post. raw also helps you deal with the crazy colored lighting which can be very overpowering and deceiving to your auto WB.
if the stage lighting is anywhere near decent the band should be nicely and dramatically lit, so the speed light probably isn't gonna buy you much. that's if it even reaches, and doesn't illuminate all the crap/fog that's usually in the air at these types of things. for shots of anything on stage i usually have the flash off. and when i forget to turn it off, i often find that it ruins (or at least detracts from) the shot. for shots of the audience, flash is extremely helpful for illumination, WB, and freezing the motion.