I can see two ways this could go.
Hollywood Version:
All the Avengers are "lonely everymans" with psychological problems.
Thor is "Lost", Iron Man is "Drunk", Hulk is "ANGRY!", Cap is "PROUD"
Sort of the seven dwarves of maleness, each will have to face their fears before they all come together for a big hug.
The "Excelsior" version:
Screw all that relating. The main magic here is the "POWER". Thor can "POWER" the Weather, Iron Man can "POWER" the Suit, Cap can "POWER" the Shield etc. so that the "One Magic Rule" can be kept intact despite the Fantasy/Sci-Fi/Pulp crossover.
That, IMHO, is how it should be played - and don't you remember Bob? Spiderman is being remade...who's to say our friendly neighbourhood wallcrawler won't be back with Shellhead and the others?
MARVEL can do crossovers well (The House of M) and REALLY badly (Inferno), but if they can keep this one on the rails, we're gonna have something that can't be ignored by the Oscars.
And if there's a Marvel...Bats, are you listening?