1. Add in maturity. Building a product and selling it is hard. You can be harder, though. this may get easier as you get older? While it's nice to have someone to support you, it is not necessary. You can be a lone wolf and absolutely kill it. It's a mindset.
2 & 3 together. External validation can/should come from outside the day-to-day. 1 person's head is an echo chamber. 2 or 3 people can turn into an even more convincing one. A small council of real customers and a regular small round-table meeting with other entrepreneurs takes care of it.
4. I believe in acquiring the skills yourself. Business and tech problems collapse into a single idea when you have all of the skills yourself (sometimes even just at an "intern" level). For capacity, this is a problem. You usually need more horsepower for bigger problems. I'd adapt this point to focus more on local outsourcing. You should be still be the architect and foreman though. So you should know how to code and mock things up perfectly.
If the tech people don't get it, it is always your fault. You have not explained it correctly or you have the wrong people. The first is more likely if you don't know how to build a web app at all or can't mock it up to the actual UI element detail. Of course, sometimes it is the latter. Just not usually. :)
founder = solo business owner in a smaller niche area. Points also apply to a much larger business I'm starting now.