Honestly, I don't understand why he expects his plan to work flawlessly now. First, he kills off a valuable ally. Yes, they don't trust each other, but still Obito's powers are useful. Now, upon arrival of four past hokages, including of course the mighty Hashirama, and Minato who has KM which makes him even more of a beast, Sasuke, soon Orochimaru with five kages, he wants to attain a living body using Rinne Tensei, a body with limited chakra and shit. Like all of those big shots on the battlefield will just watch him absorb Juubi into himself, which by the way I don't expect to be a costless process. Sealing Juubi into himself while creating a defense against the shinobi army will take a huge toll on his, now limited, chakra supplies. Even if he manages all that, why does he expect he'll be able to control the Juubi straight away? I mean, it's Juubi we are talking about, not a golden retriever or something. The way he is going now, he's gonna end up like Kabuto, standing in one place looking stupid.