I already had a different side project with 300k users so it was incredibly easy to find PMF fast because I just emailed them.
Tech choices: I never reinvent the wheel. I just take working pieces from other work that I've done and glue it together. Anything custom, I'll read how others do it.
Lessons: I probably should've chosen a different market. If I had targeted companies and taught their employees professional education rather than poor amateur voice acting hobbyist, I'd probably be making $20M ARR. But I don't mind, this is still fun.