1a. Google Translate
sry its in engrish. they seem to have edited it as well, but the enhancement level makes a difference in the values youll get as well. so higher enhancement = higher socket.
1b. from what i hear in NA forums it seems that the single stat gives higher values than the dual stat. but the dual stat just might be harder to get max values, not really sure
2.60% is the lowest that they will receive affinity. below 40% and they stop buffing as well
3. the answer is yes. if you craft weapons youre essentially taking your old weapon and making a brand new one. so any sockets, enhancements, and attributes will be gone