In the mixer, should the 'normal' volume for each track start out at 90 and then adjust from there? If the volumes are significantly lower, say in the 30-40 range, would this be why when I use MP3 Gain, the volume shows in the 70s and needs a lot of gain to reach the target normal of 90?

And again on the mixer - the volume sliders at the bottom - why/when would these be used?

Thanks.