The single-person question is an interesting one. My instinct is to say: "let's try it". Of course I begin by performing a mental simulation. And it then occurs to me that this might be expensive, time-consuming, very, very difficult (especially obtaining materials!) but most of all dangerous. I suddenly wonder how many people have been maimed or killed developing modern (manufacturing, especially) techniques. Even if it's possible for one person to do; what are the odds of survival?
Ok let's make intermediate challenges, maybe not current tech, just enough to survive comfortably. Function of some context (different paths whether you start in Africa or Russia because of material, climate and such)
- math/physics knowledge to assemble tools
- having regular heat sources
- building a small shelter
- regular nutrient sources
then there's room for
- increasingly precise and versatile tools
- finding ways to generate and store electricity (wind, water)
- light
- optics
- radiowaves/communication
