We know that he wants the 7 lights to fight his 13 darknesses and he hopes to become some God even though there is no real proof of that just a few notes but he become God anyway so we can have a awesome final boss... I'm not complaining.

Back to topic what does he want after that? when everything turms into darkness DARKNESS DARKNESS IS THE HEARTS TRUE DARKNESS sorry I had to what will he do when after that and the power of Kingdom Hearts.

It may be more complex than that. Actually, here is the thing. Should Master Xehanort be successful, everything will be sent into darkness and this time, there are no Dandelions to save the Realm of Light and rebuild it. Everything will be gone all because he wishes to know what the Keyblade War was like. That war will spread to every world and destroy everything. That is what will happen.

The Xehanort reports kinda give a good insight into his motivations for all his plans, ultimately he thinks that light has gotten too strong and wants to create a balanced world through kingdom hearts. Or at least the way I see it that's his justification, it feels to me like he's just driven by this constant curiosity to see something new.

 

Also in regards to your god comment here's an extract from Xehanort report 4:

And when Kingdom Hearts is complete, it is said the one who opens its door will bring about the creation of the Next World. Such a feat is above any human. Or, to put it a different way: whoever opens that door will be reborn as something far greater than human.

So yeah, awesome final boss fight confirmed

Master Xehanort doesn't want to be God he just wants to see what would happen if another Keyblade War would bring into the worlds. Like the old saying "curiosity kills the cat" because Master Eraqus said that Master Xehanort would risk an apocalypse out of curiosity. He just wants to see if another Keyblade War would bring balanced or something else.

We know that he wants the 7 lights to fight his 13 darknesses and he hopes to become some God even though there is no real proof of that just a few notes but he become God anyway so we can have a awesome final boss... I'm not complaining.

Back to topic what does he want after that? when everything turms into darkness DARKNESS DARKNESS IS THE HEARTS TRUE DARKNESS sorry I had to what will he do when after that and the power of Kingdom Hearts.

All I know is that he just wanna reenact the keyblade war again to satiate his curiosity...............that's it.

 

typical mad scientist stuff where scientist villain dude wanna see what this one dangerous experiment would create even if it meant he'd kill everyone in the process

According to what we've been told (by the narrative, Xehanort's Reports, etc.), a pragmatic combination of "balance" and simple curiosity.

 

But according to what we've actually been shown... yeah, just "DARKNESS!" and godhood and stuff.

Well, Xehanort says that the world is overrun by a so called "tyranny of light" and he aims to bring balance by creating a world where light and darkness are equal. And like the other members have said, and as the games have pointed it out, he's simply a curious man who is driven by the pursuit of knowledge to seek out the unknown, and since the Keyblade War is such a mythical and wondrous legend for him, he wants to know what would happen if another war was triggered. Would it bring absolute oblivion, or the dawning of a new world? Would it bring him answers, or more questions? Ultimately, he seeks knowledge and power. And I'm assuming he's going to get his hands on both, or at least get very close to doing so!

Xehanort wants to unlock Kingdom Hearts in order to be reborn as something far greater than human and recreate the World to have complete equilibrium between light and darkness.