Is there a way in Audacity to use one track as a ‘template’ to automatically adjust the gain/output levels on another track?
I tried to manually adjust the levels and seemed to get pretty close, but now I’m wondering if there’s a way to automatically do it.
Your ear is probably better than the any software. 
There is also a [u]ReplayGain Plug-in[/u] that you can use to check the “loudness” of the files.
Then after you know the dB difference, you can enter a negative dB value into the Amplify effect to bring-down* the too-loud tracks.
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- In general, you have to reduce the loud tracks rather than boosting the quiet tracks because there is a “digital maximum” of 0dB, and since the peak levels don’t correlate well with perceived loudness, quiet-sounding songs are often normalized/maximized for 0dB peaks and their volume can’t be increased (linearly) without clipping (distortion).