As it sounded from Madara, he wanted to lose the fight against Hashirama, in order to plan / prepare everything for the future.
No, I don't think so too? If he could have defeated Hashirama, could he have taken the lead over Konoha? I just think the thing with Hashiram's body was plan B, if he had defeated him he would have had his body plus DNA etc. ... That means who Madara Madara is ... he could have continued working on his plan without any problems ...
As a few have already written, it was not that easy, after all, his own people turned against him. And the way Madara sounded, he never forgave his clan for this behavior, nor does it suit his style.
It is also questionable whether the Senju would have accepted him as a Hokage, possibly a civil war would have broken out, and whether Madara would not have needed that for his plan, especially since he had no support from his clan.
Itachi Uchihha wrote:
I don't know, but I don't know what it brought him to let him live. An enemy who is almost at eye level with him (should he have let himself be defeated on purpose). His whole plan would not have been broken if he had killed him. He could have had the cells, pretended to be dead, slowly disappeared in the minds of his fellow men and could have worked on his operation undisturbed.
And his arch-rival would have been defeated. By him. The will of the fire would have suffered a severe setback. Given the pride of the Uchiha, that would certainly also be a reason.
Perhaps Madara went into battle with the intention of killing the first Hokage and taking possession of his DNA.
We don't know exactly what Madara wanted. It could be that the first one was just too strong and he could "only" get hold of the DNA.
We know that Madara lost the Kyuubi in battle.
Could that be part of his plan to lose the Kyuubi or to use him in this fight.
After all, we know what fear the village elders were afraid of this happening again and that they always distrusted the Uchiha. To sow this mistrust may have been part of his plan from the beginning, which then culminated in the Uchiha massacre.