Check out the Einstein-de Haas effect, which "demonstrates that spin angular momentum is indeed of the same nature as the angular momentum of rotating bodies as conceived in classical mechanics". Some people will tell you that electron spin is not of the same nature as macroscopic spin, but the hard scientific evidence says otherwise. Something that I think is well worth reading is Hans Ohanian’s 1984 paper what is spin? He says “since the naïve mechanical picture of spin proved untenable, physicists were left with the concept of spin minus its physical basis, like the grin of the Cheshire cat”. He goes on to say Pauli pontificated that spin is an essentially quantum-mechanical property, and that the lack of a concrete picture was a satisfactory state of affairs. He then quotes from Pauli’s 1955 essay Exclusion Principle Lorentz Group And Reflection Of Space-time And Charge: “After a brief period of spiritual and human confusion caused by a provisional restriction to ‘Anschaulichkeit’, a general agreement was reached following the substitution of abstract mathematical symbols, as for instance psi, for concrete pictures. Especially the concrete picture of rotation has been replaced by mathematical characteristics of the representations of rotations in three-dimensional space”. I think that's astonishing. Particularly because Ohanian says this: “the means for filling the gap have been at hand since 1939, when Belinfante established that the spin could be regarded as due to a circulating flow of energy”. Belinfante’s paper was seventy seven years ago. I'm not sure what you mean. Electrons and positrons get their spin ½ spin when they're created in pair production. Again I'm not sure what you mean. If the motion is different the spin is different. It's because the electron is a Dirac spinor, and a Dirac spinor is a bispinor. For an analogy, think of a disk standing on its edge. Now make it spin like a wheel. It could be spinning clockwise or anticlockwise. Lets' say it's spinning clockwise, but now lets' walk round the back of it, and lo, it's spinning anticlockwise. Now keep the wheel-like spin, and spin it like a coin as well. Which way is it spinning? It's hard to say, because it's spinning on two axes. But note that you could have spun that "coin" with your left hand or with your right hand, so there's two different ways to make this disk spin on two axes.