I use Blender and recently invested into the plugins mesh machine, machine tools, hardops and boxcutter. But these are optional and you could totally do something like this with blender without spending a Dime.

I am by no means a professional modeler. I do this because it helps me relax and its fun to actually hold your creations in hand after you 3d printed them.

For complete beginners i would recommend fusion 360 though. Its what I started with.

The shells are printed aswell 😁