I'm still waiting for someone to explain to me why in Man of Steel young Clark Kent wears a towel around his neck at the end and does the classic pose. WE do it as kids because that's what Superman (the first superhero) and the other heroes did but in that universe they don't really exist. Sure the classic pulp heroes wore capes but why red and with THAT pose? I know Batman is going to be forty something in the next film, was he imitating Batman? Does the JSA exist? If either of them exist why were people so shocked when people with powers showed up? Is Batman just fighting powerless villains for his whole carrier?
You answered your own question, presumably. Other, fictional pulp heroes presumably exist in that universe, and some probably wear capes. And the hands on hips, chest puffed out pose goes far beyond Superman, and I'd argue likely predates him.
Batman exists, but is good at his job. He's not looking for attention from the media or police, so even though he's been doing it for awhile he's largely an urban legend to everyone but the criminals unfortunate to run into him. So I doubt young Clark was imitating Batman, since it's entirely possible he doesn't even know Batman exists, either as a kid or an adult (though it's more likely he knows of him as an adult).
As for the JSA existing? I seriously doubt it, and would outright state no. If it's a big deal the JLA forms later on, I'd put that super team as being the first, hence no JSA, least not yet.
As for why people are shocked when people with powers show up, it's simple. Even with Batman running around doing his thing, as I said he's largely an urban legend. He's also still human. No one before Superman, Zod, and the other Kryptonians had ever displayed such powers/abilities to the world at large before the events of Man of Steel. Batman v Superman will likely reveal Wonder Woman and Batman to the world at large (it may also reveal Cyborg, Aquaman, Flash, etc, depending on how the script plays out and what rumors prove true). Justice League will likely reveal the rest.
As for Batman's villains, who knows? That hasn't been revealed at all, yet.
So to wrap up, you're kind reaching with this one. The questions you're asking either have blatantly obvious answers or none at all, since we won't find out certain things until Batman v Superman, or Justice League, or a Batman solo film later down the road.
So yeah, the question about Clark wearing a cape as a boy seems pretty obvious. Chalk it up to him imitating fictional superheroes of his world (or do you really think his reality doesn't have comic books and cartoons?).
