Oh… One other point I just read on another topic that is applicable here (which is why this Forum is so awesome)…
Occasionally, you can use you thumb to reinforce meloldy notes on other strings too… because the thumb hits with more weight than the other fingers typically.
So… another point for your consideration… 
Hi Grant 
Welclome to @BanjoBen 's Forum.
So I see your new to all of this and you’ must surely be wondering how does all this work. Well Grant let me reassure you, you are in the best place to learn.
As to your question, The Thumb can play ANY string. The Index finger can also play any string but not so much the 5th. The Middle finger mostly plays the 1st string but from time to time will play the 2nd & 3rd string. It all depends on what sounds you want to create. So get used to seeing TIM. Thumb, Index and Middle and many variations of those picking patterns.
In the lesson Ben is introducing students one way to play a forward roll pattern, there are many forward roll patterns, but as you need to start somewhere Ben has chosen this roll pattern to get you started. As you work through the beginners learning track he will introduce other picking patterns.
So here’s my advice for what it’s worth. Stop jumping all over the place as you put it and focus on learning the fundamentals. Work through the beginners learning track and learn the basics first, you will then have a good grounding to jump about as much as you like afterwards .
Ben has worked hard to put in place a structured learning pathway to follow. There are literary tons of amazing lessons to work though but in order to benefit you’ll need to know the fundamentals and be confident in the knowledge that you have taken the time to study them. Happy Pickin 
@Archie had a great answer, but to restate, the point I’m going for in this lesson is to simply establish the motion. I don’t want to introduce too many variables at once. If you continue through the learning track you’ll be introduced to using the thumb on other strings, thanks!
i’m having trouble speeding up stanza 7 how would you speed it up?
Hi @elaboylotr,
I am going to let the more experienced players reply to you but I wanted to welcome you to the forum and invite you to be active here among other Bluegrass enthusiasts, players and students.
Thanks for positing and let’s see what the forum participatants suggest to help you.
Hey, welcome to the forum! I want to make sure I understand your question correctly–do you mean speed up the .tef tab file or speed up your actual playing?
I have played guitar for years but now on the banjo. I’m having a great deal of trouble getting my fingers to work with my brain when plucking. When I play the song it sounds like a slow scale on the piano and not musical, and I’m able to play it slowly along with Ben on his version, but at 110 my fingers go nuts and I start messing up. Do you have any other pointers on getting going on plucking the banjo? If I play this song one more time slowly I may scream 
Hang in there! Post a short video of you playing and that will give me something to go on. There are a number of things that could be going on but we need to try and narrow it down
Hi there. Here I am playing it lol) sad rendition. This is the first link I’ve created in google. Not sure you can get it. (https://photos.app.goo.gl/QgkX4P4RGYZSVoQ77)
Hi Christopher you video doesn’t appear to be working
Ok I see your picture Christopher but the video still doesn’t play. Can you try creating a You Tube account upload the video there then post the link to the video here, If you need any help just holler and I’ll try to guide you
I’ll need to figure out how to upload the video to google and share the link. This appears to not work.
Here you go…
Using picks may help your accuracy on the strings after you get used to them.
have patience…speed somes with being comfortable & relaxed with all the movements you need to make…,which takes time…
You have the roll pattern Christopher, I agree with Dave @Fiddle_wood start using picks, Patience, Practice and Perseverance is my motto. Play it slow and smooth. It takes a while but when it clicks in your brain you know you have it.
thanks…it just doesn’t seem to come very fast. My thumb keeps trying to take over like on the guitar. My picks should show up in the mail tomorrow :).
Speed will come through time. At the stage your at you need to play dead slow. Give the brain time to memorise these patterns. I have been playing banjo 12 years and I still start out learning each new lesson slow.
After mearly 50 years of playing different instruments I still play/learn most everything slowly. I like having time to htink while I’m playing.
Check this out: