Assuming I were tapped to pen a Wonder Woman, I would also expect that it was intended to work inside the universe that Man of Steel began. Given that, I think there’s a perfect way to keep the essence of the character true while updating it to work in a somewhat more realistic world and with a more modern perspective.
I’d adjust her origins slightly. In Man of Steel, they show an open capsule on the Kryptonian space ship. In the prequel comic, it’s revealed that Kara Zor-El was the captain of that ship, survived the crash, that was her capsule, and she walks off into the distance some thousands of years ago. So I say, pick up from there, have her run into a primitive tribe, be seen as a goddess, and her off-spring as gods. This could both lead credence as to how the Greek mythology started in this universe, how they have powers, etc. I would ditch the whole pure women thing, but having Kara as the ancestor, it would be easy to see them as a matriarchal society.
From there, Themyscira is an island hidden using some ancient Kryptonian technology because Kara was wary of interfering too much with the rest of humanity, and the Amazons are just the decendents of the “gods” so they have some of the Kryptonian powers, but not all of them, which could explain Diana’s powers, and the rest could be explained with some other Kryptonian technologies, whose secrets were lost to the primitive society, and so they’re perceived as magical items, like her bracers.
Wonder Woman needs some origin story, it cannot be skipped because, while people know who she is, I don’t think many people know it well enough, and those that do, know how much magic and mythology is involved. They need to explain how it fits in with the more realistic universe that they’ve started. So, I would do it sort of like Man of Steel, give some basic background to start and fill in the rest as it’s relevant to the story.
And as for the basics of the story, I think that the best way to do it would be to have the Amazons as still fairly isolated and have them feel they need to intervene when the entire world is in danger. This was why, I think, she originally got involved in WW2. Her character should be a little like a fish out of water, not feminist per se, but more just caught off-guard that modern society isn’t matriarchal like her society.
As for her obstacle, stick with a villain. Because she’s based on Greek mythology, using Ares or Hades gives a villain that can be immediately recognizable, and if they have some of the Kryptonian powers and/or technology, given that he’d be a “god” he may still have some understanding of it, and pose a real threat. His motivation could be something fairly simple like the idea that the Greek pantheon were Kara’s progeny, much like the Amazons, but they didn’t have interest in being isolated, left out to rule over the inferior humans, were eventually captured and imprisoned, and the events of Man of Steel or something else like that led to their release and he sets about to either rule humanity or exact revenge and that’s why Wonder Woman has to stop him.
And please, don’t give her a ridiculously skimpy costume, please make it look like something an Amazon warrior might actually wear. And definitely don’t hook her up with Superman, I’d rather see her be wary of him trying to help her, seeing that he has powers not unlike the “gods”. I also wouldn’t want to see him save her nor do I want to see the cliche opposite of her saving him, at most he should help her in some way, perhaps helping prevent whatever cataclysmic event the villain puts in motion and saving lives and he’s left to help minimize that damage while she fights the villain. They can directly team up or save eachother in Justice League, but if it’s her film, she needs to be the badass.