I haven't edited a whole lot of rap pieces, but as far as shooting concerts goes, I would say go in with a general idea of what you want for shots to edit (i.e. x shots from the right, y shots from the left, z wide shots, etc) Depending on the artist/who you're shooting for, you may be limited to where you can shoot and for how long. As a result, be as geared up as possible to do a lot of run-and-gun type shooting. You are very skilled with your glidecam, so that will probably be a very solid go-to piece just to stabilize everything (not necessarily all "flying" shots).
For general advice on shooting - shoot, shoot, shoot and keep shooting. The main issue with live events is that they only happen ONCE. As a result, it is significantly better to go into editing with too much footage, rather then ending up needing a shot you can't reshoot. ( just my thoughts from experience). This is very annoying when logging footage, but in the long run is better.
Depending on the style of rap and final piece you are thinking, you could "shoot to edit." If the venue is very intimate and has the "basement hip/hop show" feel, feel free to get in the crowd and get some handheld shots in there. I have always enjoyed that slight motion with the crowd to really bring the viewer into the atmosphere. That being said, if it's a big concert hall, that may not be as appropriate for the feel - you may then want to stick to smooth movements, tripod shots, and longer lens shots.
Just a few of my personal thoughts on the matter, both as a shooter and as a viewer.
This is by far not my strongest piece. Here is a little side edit I made from a Brother Ali concert I covered as part of a larger project last year.
I also remember Alex Horner shooting a piece on Macklemore a few years ago that captured the energy pretty well. I'll try to track that down as well.
Hope this helps,