That's gonna depend on your skills and what you think is interesting to pursue. Generally speaking you'll want to learn how to, at a minimum, model stuff and 3

That's gonna depend on your skills and what you think is interesting to pursue. Generally speaking you'll want to learn how to, at a minimum, model stuff and 3d print it, and how to design PCBs. I strongly suggest FreeCAD and KiCad for those tasks respectively.