I shoot concerts on a regular basis with varying light conditions. Mostly jazz artists and the lighting varies from very well lit to not much light at all.
I shoot with 2 Nikon D300 bodies and own one of the lenses you mentioned (18-200 VR II). Your 50mm f/1.8 will work fine, but won't give you closeups. Your Tamron 90mm f/2.8 will be good enough most of the time, but you will be shooting wide open.
The lenses I use most often are: 70-200 f/2.8, 300mm f/2.8, Tamron 28-75 f/2.8 and a 85mm f/1.8. Occasionally, I'll use the 50mm f/1.4, but only when really close to the stage. On the D300, the noise picks up considerably at ISO settings above 800. I tend to shoot at 1600, with a white balance set to 2700 degrees Kelvin. My typical exposure is around 1/40 second at f/4. Shoot in RAW mode and use the histogram display and the "highlights" turned on. I'll meter using the spot meter setting, then adjust the exposure based on what I see on the histogram.
In all the venues I shoot, flash is strictly forbidden.