Regarding burn out: building a solo business can be hard and chaotic work. I think the key is learning how to prioritize and getting comfortable with many parts of the business being broken or incomplete. There's always more to do, and you'll never finish your todo list.

So practically that might mean ignoring certains bugs that are not crucial, being okay with some design issues, "firing" customers that take up too much of your time, limiting your availability to certain people (especially people that want to chat without a clear goal).

I also think each project can feel different. Some feel like an uphill battle, while others almost pull you forward. It requires having worked on multiple projects to develop a solid awareness of this. So feel free to experiment with different ideas and compare how easy or hard they feel to work on.