It won’t leave you financially ruined if you treat it as a side hustle and keep your main job as a source of income until you get customers.
And if it never takes off, so what? At least it will be a great learning and self-growth opportunity, which is exactly what the OP is asking for anyway.
Thank you for your comment. I often feel that a part of HN judges jobs only based on income and blames you for not focusing on one or the other and thereby losing out on income or business growth.
However I, too, think that it's completely valid to stay at your main job while also working on side projects. Maybe you won't be the richest person in the room or turn your project into a huge success but being able to do stuff you love while not risking your peace of mind is worth something as well.
And if it never takes off, so what? At least it will be a great learning and self-growth opportunity, which is exactly what the OP is asking for anyway.