The best way to learn is to do because learning requires tight feedback loops. You have more or less the correct idea with these steps, however they should be

The best way to learn is to do because learning requires tight feedback loops. You have more or less the correct idea with these steps, however they should be weighted (and continuously re-weighted as you progress). I would add an additional step 0: commit to yourself that this is something you're going to see through. Do you want to start something because of a sense of FOMO or because you genuinely enjoy creating? Are you ready to quit your job and start, having the confidence in your tenacity? Importantly, your internal motivations will inform the amount of weight that should be put into each step. For example, if you're building something to solve a problem that you yourself experience, steps 1 through 4 can be weighed at 0 and 5a (5 should be split into distinct parts) should be weighted at 1. Assuming the behaviors which give rise to your need are distributed, within the general population, on a bell curve and you fall somewhere within a standard deviation of the median, you are your average customer and don't need to prove the market ahead of time. Overall, YC's advice to "build something people want" is spot on. Do that systematically and everything else is more likely to fall into place in spite of your weaknesses.