Well I think Itachi is one of the most -if not the most- genius people in all the Narutoverse.
About Izanami being activated or not.. I really think it has been actually activated, but I don't have any idea on what might be the destiny he wants to get.. maybe something related with changing Kabuto's ideas / past-future identity / etc...
The Tsukutomi thing.. I don't really know, but I wish it is some kind of advanced Tsukuyomi that needs a combination of 2 Mangekyou Sharingan to be activated - I don't think it is a mispelling or at least I don't want it to be a mispelling
About Itachi being cut in half.. well I think it just fits what he clearly said in front of Kabuto in the beginning of the fight that he will make Kabuto under genjutsu and know how to stop the Endo Tensei, and that Tsukutomi and being cut in half and the talisman with Kabuto are all part of the plan.