I designed a custom shape for something I needed for another hobby (holding a first-surface mirror at 45 degrees so I could try to learn to paint by copying) and that was really satisfying to learn 3d modeling and making a real object. I should probably do more things like that, such as making a robot or something.

I have realized I already have more hobbies than i have time for. I do need parts to repair my other hobbies, I might get a 3d printer for that, but i'm thinking about using some printing service to make parts for me instead

A good 3D printer isn't a very large time-sink.

But it's only worth it if you have a reasonable number of those parts, or if lead-time is important. For most people designing stuff, led-time is essential, but not everybody that want some specific part designs it.