1. Solo founders are most often devs, which means they focus 90% of their energy on dev and what little remains on marketing. Unfortunately this is a easy trap to fall into and you should invest equal if not more time doing/learning SEO, content marketing (which you've done here very successfully btw) and building an audience.
2. Making a product without any user feedback. You work 1 year on a product and realize people don't get your idea. That's why it is essential to get feedback every step of the way and your spouse doesn't count :D
3. The good news is being a solo founder is no longer very unique thing. There are hundreds of thousands of people who are doing this and hang out on online communities like indiehackers, makerlog, etc.
4. After trying out hundred tools I've found that nothing beats trello. To each his own though but you really need a todo tool when working alone to keep on track. I've actually written a local trello for myself with one twist - the tool assigns me a task daily and as soon as mark it as complete it assigns me the next item from the list. But at any moment there is never more than 1 item on my "doing" list. It was because i was spending inordinate amount of time bike-shedding when i don't have one single todo.