Great read Omer! I’m sorry it didn’t work out for you guys.
I’m gonna say that after what I’ve read, the biggest mistake I saw was with that 3rd founder. The fact that he expected to keep all of his shares and exit at that stage was foolish. Good founders / entrepreneurs understand that 3-5% of something potentially taking off is better than 33% of nothing. Regardless of legality and for the sake of the company, I would have negotiated something like that so that the company could continue to grow. I’m not sure if he was ignorant, too prideful, or just too angry that you guys were trying to push him out. I really hope this guy learned something here (it sounds like you have).
Other than the above, most of the mistakes you made were pretty normal and you guys probably still could have succeeded. At my company, we didn’t collect much user feedback until about 2 years in and we’re cashflow positive, growing every month, and can support 15 staff. Advice that you read like that is very helpful, but it’s not always crucial I’ve found.
Anyway, best of luck with the next venture!