uhm sorry i might used the wrong word there, with "his influence" i mean "naruto's influence" (sry i think its my fault my english isnt that good :P)
and Oro did say that! not me...
and the body transfer does not need special preparations it does work very fast if you rewatch the episodes right before Kabuto sends Kimi you can see it. or at least these preparations were allrdy made at this point

and the reason why Oro did not take over Sasuke's body in the jungle is simply because he wanted to test him... he wanted to see if he is worth the effort and here again, its not me who says that, its Oro himself.

(btw that is true "evidence" :P)