Looking for guidance on a small hobbyist project that could eventually scale upwards

I'm a data engineer with a few years of industry experience, and I had an idea for a little webapp that I think could have some real practical use. A friend of mine recently graduated from a full-stack bootcamp, wants to build out his frontend portfolio, and so is down to work with me on this project.

I was wondering if there are any helpful books or guides out there to help me get a better sense of how this project should progress. For example, in what order should be defining use cases, making wireframes, getting code written? What are some low-budget product management tools that would be good for a team of two? I see this as a hobbyist project, and have no plans to turn this into a business or anything, but I could see this eventually being used at some fair numbers, like maybe a few thousand people. Since I do want to take this seriously I would love to know how to get the most out of the work I put in.