Marvel-Disney pulled off an astounding balancing act with the outsized success of “The Avengers.” But can they do it again?With the superhero team-up well on its way to $1 billion worldwide, Disney CEO Bob Iger surprised absolutely no one Tuesday when he told shareholders that a second helping of “Avengers” is on the way. It’s a no-brainer, to be sure. But it’ll take super-human stamina to make all the pieces fit together again. At the top of the to-do list is booking Robert Downey Jr., who initially signed on for four turns as Tony Stark in a deal that carries him through next year’s “Iron Man 3.” For the next “Avengers,” Marvel-Disney will have to reup its centerpiece character with a deal commensurate with the inevitable success of a second “Avengers” pic, which likely means a hefty backend haul. Other “Avengers” stars — including Chris Hemsworth, Chris Evans, Scarlett Johansson and Jeremy Renner — have signed deals that go beyond the three-picture pacts that have become industry standard for tentpole franchises. Samuel Jackson, for example, inked a nine-picture deal, and most of the other main actors have signed on for six. Next is the question of Joss Whedon, who’s widely credited with keeping all the elements in balance on a critically lauded project that could have easily gone haywire. Marvel topper Kevin Feige has shown a willingness to take chances on new helmers — Jon Favreau is the only Marvel movie director to get a second go, with “Iron Man 2″ — but reupping Whedon would buy a lot of goodwill with fanboys, and help keep the peace among the constellation of stars who now have good reason to trust the helmer. Feige will be under tremendous pressure to do it all “the Marvel way,” which means keeping a close eye on the bottom line. “It means questioning every cost, every dollar,” Feige told Variety earlier this month. “We don’t take any of (our success) for granted.” That would include successful time management, as Marvel is also developing Ant-Man, Doctor Strange, the Inhumans and Guardians of the Galaxy as potential new franchises, with potential spinoffs of the Johansson, Renner and Jackson characters from “Avengers.” Already engaged are “Iron Man 3″ and sequels for “Captain America” and “Thor,” dated through 2014. That means an “Avengers” sequel would most likely come in 2015 — if Marvel and Disney can keep all those plates spinning.