Berserk

>Since he was a priest
Maybe I just forgot, but where was this revealed?

Berserk has a lot going on that speedreaders to fail to understand because it isnt all explicit in in your face which would ruin the purpose of manga being besides a vidual medium also a narrative one, of an overall tragic type, even if it stopped being all dark and edgy.
I also didnt get all this stuff on my first read and I also kind of didnt like that much millenium falcon and specially what we got of fantasia at first. Lots of parts of those arcs felt aimless. But on my second read I saw how it all was tied together. Even if Miura didnt have everything planned at first and made stuff along the way, I think by the end of Lost Children he was already planning out a big picture in detail.
It really sucks that he died just before everything was going to hit the fan and pay off.
It just sucks in general that he died. I havent seen any art in any manga being as good as his. Vagabond is very cool sometimes but the realistic style isnt really my thing and the story and pace wasnt that great. Really liked the Kojiro arc tho.

When they are going to rescue Griffith, either Charlotte or someone else tells the story about how a priest was so angry at the king (skull knight) and his reckless nature (or because he tortured him or something like that) that some angels appeared and ruined his kingdom and killed him. When they are going down the tower they see a lot of human bones and skulls with the sacrifice mark. Then in Fantasia the smith gives Guts a flashback of how the previous user of the armor died, holding his loved woman and Void is there along with different members of the godhand to the ones we know (the angels of the legend told before) Then Skull night tells him that what he saw was the end of a foolish king. Skull Knight admited he once was the user to the berserker armor when Schierke asks him if that was the case.
Void also has 6 fingers which some user some time ago mentioned it had religious or mystic symbolism. Look it up.

bluetooth

it was hinted a long time ago

we don't know and never will because the only person that (maybe) knew is dead

His goals and the goals of the god hand are beyond your comprehension. Because they are not human. Or maybe they are more human than we are. Regardless, They transcend the morals of the physical world, aswell as the causality of the world. Meaning that their goals are not "goals" at all, rather they are more akin to rituals.

Humans unknowingly created the IoE by wishing for an answer to their suffering, IoE invented the God Hand to perpetuate suffering and the fulfillment of human desire. God Hand exist to do as thou wilt, fulfilling their desires and desires of the collective unconscious of humanity, Void likely invented the Holy See, answering Man's wish for a God, and Griffith exists as humanity's ruler, answering man's wish for a Messiah. The God Hand's power scales with the power of human belief, since their power comes from the IoE in the Abyss. The Abyss is simply a mass of souls toiling and suffering forever, so the more suffering there is both for the living and dead, the stronger the God Hand is, all the God Hand wish to achieve is their goals, and to that end they require more power, so Void, like any other member of the GH (including Griffith), wants to spread suffering to gain more power and pursue their goals further.
on the surface, Griffith seems to be a bit at odds with this since he wants to protect humanity, but he only wants it as long as it's HIM ruling humanity, it's a completely selfish desire, he has no love for the people of Midland, let alone the world. Void plays his role in controlling the world, as does Slan, Ubik, and Conrad.
I know you asked what Void's endgame was, but the answer for that is the same as every other God Hand, so you can't really talk about one without the others.

Um, it's xis sweetie.

having hot sex

to expand on this a little bit, any time you ask what any God Hand's goal is, simply look at their actions since they end up doing what they always wanted to do as a human.
Void manipulates the world -> he wants to become the master of causality and time.
Griffith manipulates humans into following him -> he wants to rule the human world.
Slan jerks off to pagans having orgies and probably gets down with them herself -> Slan wants to experience constant depravity.
Ubik manipulates people's dreams to shape them into monsters -> wants to sew as much chaos and discord in the world as possible for fun? this one I'm not so sure about.
Conrad spreads disease and famine on a whim -> also not so sure about this one, perhaps Conrad has a deeper hatred for humanity and wants to see it suffer.

To kill Berserk