For me it works best to start a project in such a way that it is easy to get back to. Fully expecting and embracing getting bored and leaving it gathering dust for a while.

For this to work I have docs folder with a todo.txt, architecture.txt, questions.txt and features.txt. I push it early to a private gitlab repo and use a language like TypeScript that makes it easy to come back to and make changes without fear of braking things. It won't be the first time that I get excited (again) by something and can continue on an existing project.