@@Kenpachi won't be reborn with his full power. Nozarashi will still be linked to him since it's a Zanpakuto, but he won't be able to use all of his powers at the start. Reiatsu won't be replaced by Ki, Kenpachi will have both since i did say he would be OP.
I don't think a harem is possible since Kenpachi isn't really interested in women, but who knows! If many people ask i think i'll be forced to give Kenpachi some girls, even though the story will still focus on fighting.
Be aware that Kenpachi won't change his personnality, he will do anything for a good fight. He's like Saitama but way crazier.
The story won't always be focused on Kenpachi, as sometimes i'll talk about other characters or the situation in other places of the Universes. The P.O.V might change sometimes but i'm not entirely sure.
If you have anything you want to say to me, just write it in the comments and i'll answer everything=)