I'm also planning a Superhero party for my 4 yo old but we're having ours at home with only 8 children.
We're also doing pin the cape on the superhero and when the children arrive there'll be a craft table where they can decorate a superhero mask and I may get them to decorate there own going home bag with their initial in a shield (like the S on Superman's chest). I'm also trying to work out some kind of treasure hunt. There'll also be pass the parcel and other non-themed things like musical statues. Will also play sleeping superheroes towards the end to calm them down.
As ours is at home my main priority is to go for quiter activities but you have space to let your guests run around.