This really should be a full-on, Superman Man of Steel sequel with a hint of Batman at the end, as much as I hate after credits scenes, leading to a Batman reboot. And after that, a proper World's Finest movie again hinting at another character: Wonder Woman. And then she gets her own movie leading to Trinity. That would be my "Phase 1" DC cinematic universe. Save Flash, Green Lantern, Aquaman (yes) and possibly Martian Manhunter for a Phase 2, maybe 3, THEN Justice League.
You're dealing with more core characters than Marvel (Cap, Hulk, Thor and Iron Man) so obviously it's going to take more time to set up, and if you do it right, it'll be more than worth it. They could really kick Marvel's ass at this, because there's a lot you could do better. DC is acting oddly headstrong ("Let's put everyone in MOS 2!") with characters they think need more reworking than they need. If Thor can f**king work so can Wonder Woman, Aquaman, etc.