You can try using the "normalize" function to bring up the volume. WRT track bleeding, in MP3 encoding there is a mode called "joint stereo", which merges the two tracks into a middle track. If you are encoding stereo at 128kbps, it's likely using joint stereo. I can't find a way in Audacity to control this setting.
Search this link for "joint"....
http://www.oreilly.com/catalog/mp3/chapter/ch02.html