I disagree with basically everything you're saying, but yeah i remember when we used to be on this thread all the time before everyone had been cast. Michael Fassbender, Ryan Gosling or Jon Hamm were my Batman picks. So glad they went with Affleck instead.
They don't NEED to use Brainiac for the first film. He would be a good pick, but I'd be just as happy if they saved him for a later Superman film. Perhaps Superman is taken prisoner aboard Brainiac's ship, along the lines of Superman: Unbound. That way it'd make sense for other League members not to be involved. A self contained story with a threat as large as Brainiac would have to explain why the other JL members were absent, and Clark being held prisoner is the perfect way to explain that.
Also that's not the Suicide Squad, it's the Legion of Doom! Of course they are a match for the Justice League. I'd add some more muscle to the team, Metallo would be a good fit.
Lex Luthor
Joker
Harley
Deathstroke
Manta
Cheetah
+Metallo
That wouldn't be a threat to the Justice League? It would, and i think it'd be better if they went with the Legion of Doom for Justice League 1, then Darkseid for Justice League 2, with Brainiac for MOS2, and Doomsday for MOS3.
Legion of Doom leading into a Darkseid storyline could end up being structured somewhat like the Rock of Ages storyline
I've gotten attached to the idea of SS setting up a Legion of Doom/Justice League movie
Also it really doesn't matter what gender Brainiac is, Tilda Swinton is perfect for Brainiac..
Santoro is also perfect for Darkseid, his voice is completely ideal for the role. He could voice the role, and some massive dude could play Darkseid practically, with lots of CGI enhancements
Also don't know why you're against Jackie Earle Haley being in this universe, he's totally ideal for genre stuff like this. Desaad would be right up his alley.