I have a somewhat contrarian perspective to your #1/2. Instead of starting with an idea, start with a market. Maybe even a problem in that market. Then go out and have as many conversations as possible with people in that market to really wrap your head around what problems they have and how they currently solve them. Only after that, start testing solutions to their problems to find marketable products or services. The 'idea first' mentality so often leads to confirmation bias.
Lastly, as a full-stack engineer who has made the transition into 'successful' full-time startup ceo, I advise to to focus less on the technology than on the sales and customer relationships. Tech skills will be your competitive edge, but personal relationships will be the foundation of the business.
Others mentioned MicroConf. The organizer of MicroConf, Rob Walling, wrote a book where he gives very similar advice: https://www.amazon.com/Start-Small-Stay-Developers-Launching..., both around starting with a market and focusing less on technology and more on sales. He is writing for a particular niche of smaller, non-VC-backed startups, but the general approach still seems similar.
Lastly, as a full-stack engineer who has made the transition into 'successful' full-time startup ceo, I advise to to focus less on the technology than on the sales and customer relationships. Tech skills will be your competitive edge, but personal relationships will be the foundation of the business.