It'll take a bit longer for Superman to be up for interaction due to not being Superman yet. Once this initial arc is over, he'll be down for some collabs.

Hulk, I don't know yet. I'm still trying to figure out where to go with him in the beginning. 

Granted, even a recently born Hulk is a lot to throw at anyone in this setting right now. I'm playing the only other character who might match him on a pure durability level. So maybe I should just isolate him for the moment.