I have found that all of the songs in Ben’s collection of lessons has something valuable to teach in each one. So I would go through the basic lessons and pick a song that you like the sound of and learn that.
My second song was Rocky Top but I have to admit that it took me a year before I could play it somewhere close to speed and only now, at 16 months that I can make it more or less sound okay!
In Coming Round the Mountain, playing the four notes of measure 3 TITI (T= thumb, I= Index) would be the most conventional way of playing that measure with the C in measure 4 played with the index.
Now you could use your middle finger to play that C note too. In later, more advanced lessons, Ben discusses about and uses the middle finger to play the ‘inside’ strings, that is the B and the G string (the 2nd and 3rd string) which is quite daunting for many beginners as we get very used to the fact the in general (as beginners), our middle finger only plays the 5th string.