The starter is just live yeast you keep as a pet! You may have to change any liquids you add into your bread but I did all my bread by feel and how it was acting that day.
I think most places don't bother with the yeast in the dairy section any more, was always super hard to keep it current and not moldy but look there too next time you go to the store. Used to be in a box of cubes by the eggs or margarine, kept cool.
I'm not super happy with this site and my virus scanners but it's not so bad...
https://cnz.to/tips-tricks/convertin...dough-starter/
The King Arthur site is good but maybe not the best "how to convert my starter into product".
https://www.kingarthurflour.com/reci...starter-recipe
A lot of their recipes also add fresh yeast... I'd maybe only do one proofing with just starter. I think that would be fine for the type of bread you are describing.
I did start my Herman from that recipe before with no yeast. I messed with Herman about every 3 days, stirring or feeding or cooking or just looking in on it. Depending on how much starter you use means how much your feed it. For Herman once I got it going, I just fed it equal amounts of flour, sugar, and milk on a semi regular basis depending on the temperature and how much I was cooking. You do want to have at least as much available space in your container as you do product, sometimes it froths up pretty intensively!