The key to live events is using the fastest glass (i.e. largest maximum f/stop) possible. The 50/1.8 is fast, but its autofocus performance isn't the best; it tends to hunt in low light.
The 18-135 f/3.5-5.6 is basically useless for live bands. It's f/5.6 at the long end, and even f/3.5 at the short end will require you to use very high ISO sensitivities to get decent shutter speeds. Not saying you can't try, but in my experience with event photography, f/2.8 is the bare minimum. You'll find that most venues will be at best f/2, ISO1600, 1/60, which is pretty dark. Hence the need for fast glass.
Would suggest you start out with the 50 f/1.8 and see how that goes. If the AF performance is ok for you, then you should be fine. If you can, try to rent an 85 f/1.8 (which has stellar AF performance) and/or a 35 f/1.4L (for wider shots).