I like your ideas, but I'm unsure about using Darkseid. I'm not sure how well he would work, at least for a reintroduction.
I think Brainiac would be an excellent choice, and would also allow subtle reflection on the Superman origins if he is Kryptonian as has been done of late.
My reasoning behind Darkseid is that he's menacing and alien in appearance but ultimately human in mind and goal. His army provides a constant external threat to the people of Earth and gives the various military forces something to do so it doesn't look like they're just sitting on their butts waiting fro superman to save them. And, most importantly he's powerful enough to justify some cool fight scenes.
And by cool fight scenes, I mean supes rushing him at superspeed, uppercutting him with such force that he's literally knocked into orbit, supes flying after him, grabbing him, and throwing him to the ground (aiming for an uninhabited desert) and heat visioning him constantly as he falls. And then, when the dust clears, there's Darkseid standing in the middle of a giant crater, smiling. "Is that the best you've got?"
Brainiac isn't a powerhouse; he's a tech villain. It is fairly difficult to remain true to the character and justify a scene where he and Superman beat on each other using decomissioned WWII battleships as clubs. But there is something to be said for the coolness of a scene where two very strong guys just repeatedly hit each other with battleships.