Pamela, I think you don't realize that you have selected a topic (the evolution of tunes) which will be quite a challenge to research and to teach. For one thing, there are many sets of lyrics with no tune. (say on broadside sheets). For another thing, when someone collected a tune, it was hard to say whether the tune had been around five years or two hundred.

I think you should get confident with the lyrics part of your class first, then move on to tunes after you have done a lot of reading and learning.

And unless all your students can read music and know basic music theory, it will be impossible for them to discuss tunes intelligently. In college, I planned to take a music history class before I had ever had a music lesson. I found it so opaque (What does he mean by anticipating the 10th?) that I dropped out immediately.