You are right about half the Madara power but I disagree with the zetsu clone for the most part. See, the reason why the manga has paid special attention to Muu is that he is an illustrational counterpart to Madara. A beast of a kage, shrouded (as opposed to masked, BOTH ARE SEEN BANDAGED AS HELL), is split in battle (with a representational sibling, the younger tsuchikage who he knew, similar to uchiha+senju=siblings), BOTH are muu, one is defeated, fooling all who saw ala Madara vs Hashirama. It is revealed that the technique splits the power in half. This is why Tobi's ocular prowess is seemingly limited. We have reasons why he has not used MS but in this split theory we have bases covered for why we have 1 eye from the Madara/Izuna ems set in Tobi (see my other posts) but no real power to drive it to it's full potential. The zetsu stuff came later and we do not know the full extent of Tobi's "zetsuness" but the indications from fragments of face to the mizukage's supposed appearance is that it is a human face, not "plantish human". Zetsu is a part of the plan but not some mere clone or recepticle for Madara's soul. Zetsu is the physical enablement of Madara to have Hashirama's power.
http://www.mangareader.net/93-57473-...apter-510.html I present you this scene to begin the answers. One half Madara died to afford the other half Madara the decades/centuries needed for their crazy plan, which includes obviously now the coming up of Nagato (Uzumaki & Uchiha Madara/Izuna bred as I read somewhere here earlier) to resurrect the dead half Madara. Madara needed to be believed dead first to remove the immediate threat of Hashirama's opposition to his plans, and second the senju determination that runs contrary to his own. Run with that and you will start to have less questions and more answers.