1) First question.
Not possible to login twice for the same Wow account, but yes if ur referring to the same battlenet account but different wow accounts ( 1 login to wow1, another login to wow2 )
2) If (1) answers your question. Then im assuming you're asking if buying only vanilla for wow2 is possible. Answer is yes.
3) Title Answer
Botting is never safe if u link ur accounts, risks are increased if u have large amounts of gold ( meaning you use the auction house to get massive gold, selling ur mats herbs w/e w/e etc )