1. im guessing he's some sort of infilitrating, multiple spawning, shapeshifting venus fly trap thing O_o
2. i doubt it since the samehada and kisame share the same chakra, they wouldnt notice him within the sword due to the cloak of the same energy
3. when did it say that the sword didnt notice him?
4. itachi probably knew, thats why he made an amaterasu trigger when sasuke laid eyes on madara's sharingan
6.i dunno, i suppose we'll find out soon enough but i doubt it has something to do with kakuzu.
Something i've just realised, if you remember before the kage summit arc, shibuki (leader of the waterfall village) and his dad came to konohagakure to talk to naruto or w/e, it can't be a coincidence that they randomly appeared and now kabutomaru is infiltrating the waterfall village.