I have a small side business selling 3d prints, creeping up on 2 years old. It's roughly break even, but that's mainly because I rented a space for a studio to do the work in. I mainly sell others' models (either open licensed, or commercially licensed, and intentionally steering clear of others' IP). Slowly I'm building out additional automations to facilitate scaling, but I'm really in no rush. (Day job is great)