Well, if I was in charge...
- First of all: NO origin movies, unless it's a hero's first film like Wonder Woman. Enough waste half movie retelling the hero's origin. Tim Burton's Batman was not an origin movie and was well-received.
- Secondly: If you want to adapt a comic-book storyline, choose carefully. Maybe your second Superman film, which is meant to set up the universe, shouldn't be a story where he gets killed off. Maybe you shouldn't build your Batman upon a storyline where he is DECONSTRUCTED. Maybe Batman shouldn't be operating for decades if you have plans for his sidekicks.
- Thirdly: No one says the Donner films were perfect. No one says every Superman film must be a perfect copy of Superman the Movie. No one says Superman's stories can't be dark or he mustn't be challenged physically or ideologically. But don't try to write a dark, gritty Superman story unless you understand the character's core and you know what you're doing. Oh, and don't EVER diss John Williams' score if you want me to take you seriously.
Regarding the films:
- Superman is already working for the Daily Planet and operating publicly. Lois, Jimmy, Perry and Kara are part of the cast. And for God's sake, use someone other than Luthor, Zod or Doomsday. An Superman: Brainiac adaptation is too ask for?
- Batman started out his career no long ago and he's mostly an urban legend. Though he already has two sidekicks, Dick Grayson and Barbara Gordon. For the sake of world-building, they can reference the Super-Family every so often.
- Wonder Woman's movie was a good setup, although I'm not a fan of Diana losing faith on humanity and quitting for one hundred years. If you want to introduce Donna and Cassandra keep it simple, for God's sake. Donna being Diana's little sister is the less convoluted origin, and being friends with Kara, Dick and Barbara is a good way to set up the Titans.
- Justice League - Once the main players have been introduced, it's time for a team-up. I'm a Original Seven kind of guy: SM, BM, WW, GL, TF, AM and MM must be the founding members, IMO. If diversity is needed, get a black man playing J'onn or get Vixen joining the team.
- Teen Titans - I think New Teen Titans' introductory arc may work, if modified: Robin, Supergirl, Wonder Girl, Batgirl, Aqualad and Kid Flash are friends. Raven recruit them, Starfire aaaand maybe Cyborg to fight Trigon off.