I'd do three, a trilogy.
Have the first one start off with Supes, Bats, and W.W.
Darkseids the villain. He arrives on earth alone, not thinking any would dare challenge him.
Metropolis, paradise island, and gotham is the setting. With bits of Apokolips thrown in.
Superman and Darkseid fight, Supes loses in a close one.
Batman sees the fight from wayne manor and rushes to Metropolis.
W.W. see's the fight as well, she was in Metropolis on military business as Diana.
she takes on a weakened Darkseid and drives him off, while Bats retrives supes.
Darkseid retreats, for now.
The film ends with the villain and heroes in pretty much a draw and with Batman investigating reports of other heroes in the world. He seeks them out for help.
2nd film. introduce the Flash and G.L.( Hal Jordan)
More Darkseid, with a few of his minions sprinkled in for good measure.
more destruction insues, this time across the U.S. and canada.
Kalabac sp? and W.W. go all out. She wins.
superman, G.L., Batman, and Flash take on other minions and defeat them.
Darkseids furious, he vows to return with his full army..
It ends with him preparing an all out invasion of Earth.
3rd. Introduce M.M. and Aquaman/Arthur.
All out war between Earth and Apokolips. land, sea, and air.
Darkseids entire army invades Earth. Major destruction throughout the planet.
Barry Allen killed, enter Wally West.
Darkseid gets the upper hand, and just when it seems Earth is lost, G.L. corps arrive and take out the invasion force, but at a high cost. over half the G.L.'s are killed.
Superman and Darkseid have a final standoff. Supes cuts loose completely, defeating Darkseid.
Joy, hope, etc etc returns.
Never happen, too expensive. I can dream though.