He's gathering the biju just to control them all together, so this time the atack can be powerfull enough and it's not going to be defeated like a guy like minato again.
He wants to make sure, once an for good that no1 lives after the atack, and that the sort of ultra deamon beast he's making is not going to be able to be sealed inside a host like naruto this time.
Madara, with all the truths he knows, all the secrets, all the jutsus, and the amount of time he has lived, makes him a very dangerous fella.
There is a saying, the devils knows more cuz he's old than for being the devil... it fits madara perfectly on my opinion, and then he's not gay, he's ULTRA GAY when he's plotting and conspiracing that long xD u have to be a bastard to be that kind of a maquiavelic character XD
ULTRA GAY XD