Making tools is almost a right of passage as a woodworker or a metalworker (even for amateurs like me)!
I have greatly enjoyed making and restoring tools. I think that restoring old and broken ones is probably a good entryway into making new ones. You learn a lot of the same skills in the process with a model to work from. You can also get broken tools for cheap on-line, or in recycle shops and the like. You asked what tool you should start from, but
the answer to that is certainly the tool that you need! So what tool do you need next?
My friend is a luthier (a musical instrument maker). I spent a decent amount of time wandering around his workshop asking lots and lots of questions and he showed me how he does a lot of the process. His specialty is hammered dulcimers, but he makes a variety of other instruments as well. I think traditionally if one wanted to become a luthier you would become an apprentice to an accomplished master-worker. These days there is so much information on the internet that basically anyone could start.
If you want to get into musical instrument making I would recommend starting with a tongue drum. And then moving onto a zither. The tongue drum is all
wood, but the zither requires some hardware. Typically luthiers don't make their own hardware, but order it from specialist companies these days. So I don't know how you for example forge a tuning peg or a steel string, but I'm sure it is within the reach of a professional machinist, so the information must be out there.
Tell us more about what you want to do in particular and maybe we can point you in the right directions.