[breathesalt]

I'm in an uncannily similar situation as yours but with a part-time job. Find a job that is aligned with your ulterior goals and that provides you the time to complete them. Let's say you want to finish a machine learning textbook, then find a job that gives you enough freedom to apply that at work. Applying what you learn, at work, not only reinforces your learning but pushes you to reach your long-term learning goals. As for the prototype, the problems it's designed to solve ought to be compelling enough.