About the Byakugan?? I remember he met Neji in the chuunin exam but he never activated and demonstrate to him or anything. Everything after that, Sasuke never met any hyuga.
Ok this is legit I guessOrochimaru most likely knew of the byakugan, and then Sasuke was from the village. A lot of people knew of the sharingan before they encountered a user because people told about it, so the byakugan shouldn't be any different.