Thank you! That makes sense. The client does have some understanding about the scope of the project, since when he approached me he stated "I'm not sure if it's something for 1 person", but yeah, the timeframe would probably be an issue and I need to push it to cut it to the essential features first and add anything non-critical later.
However, is a 1 year timeframe something common / acceptable in the industry? I don't think everyone is hiring sub-contractors and it's rather hard for one person to deliver anything substantial in 1 year unless they work overtime like 50 - 60 hours per week.
This is my plan now, launch a free product and use it to promote myself as a contractor or consultant. Commit to some time spent on maintenance weekly and consider it as part of the marketing time. Maybe I will be able to monetize it in the long term, but in the short term, I need it to escape the bottom of the barrel I am currently at. You don't get to have a good resume when you are tinkering with products on your own... and I realized that especially in this job market, I can only make decent money on my own. It helps that the product is quite technically complex, gives me ideas for blog posts and the idea itself is already validated (as a free product), but the existing implementations are poor. And I absolutely love developing it.
The big lesson for me is know what you are getting into. Look at the OP - he spent every spare hour he had. This is no joke. I have done something similar in the past for a time and I ended up constantly running into conflicts of priorities between that and personal life. I ended up wasting a few years, in both personal life and professional life, although the former hurts much more. This is how I ended up in a scenario where I have nothing to show and nothing to lose. I just hope I can do it all at some 50 hours per week total, where the product is just a part of the day job (promotes the consulting offering) and lower the volume of paid work as I need, if I want to have more time to make a big move with the product.