How to adjust volume within a single track?

YES! Thank you! When I first started audio recording I used a bootleg version of Nuendo and you could do this in it. I've been wishing it was possible in Logic for over a decade and now I regret not knowing this over a decade ago!

Yes you can. Click on the "Automation" icon at the top. That will expand your track and show you a horizontal line that runs from left to right. Click on the line and a point appears. It should show 0.0 which means that you are currently at 0 db. click on the line at another point. Then move the second point down or up to decrease or increase the volume. You can also "automate" panning like this. Clicking back ont he Automation icon hides this information.

To add to the tips… Make your right tool the marquee tool in Logic. Now when you are in the vocal track and in automation mode, hold Command and you'll get the Marquee tool. Drag a box around the phrase you want to adjust, release command (returning to the pointer) and click on the selection. Now you'll have 4 nodes or handles. Drag the automation line up and down to taste. I manually "compress" all my vocal tracks with an automation pass using this trick.