Multiple Man should be fine-his powers don't make him invincible, nor do they make him really godly powerful. He's very useful for street level destruction, but once you get into the actual Iron Man level people, quality definitely reigns over quantity.
Let me start the rest by saying that no one in this tourney is getting cut down. If you pick a guy, his maximum levels must be within the caps. So while Human Torch's normal blasts are below Iron Man level, his Nova Blast would not be. Intangibility is being left to the contestants. Mind switches are a no no, time traveling will be ruled as a ring out against you. (so someone who CAN time travel isn't necessarily banned, but trying it would simply remove you from the fight, and put you down one guy) I'm probably actually just going to enforce LP's imaginary "no instant kill" rule, to make it a little easier. If you're picking someone because they can take someone of Thing level killability, via any method, in one easy go.... Don't even try it.
I'm thinking about actually enforcing the power caps as well. The past solutions have mostly been to simply adjust what one character "should" be able to do according to the tourney, and restricting them to that. I'm thinking about just eliminating characters from teams if they are argued to be well beyond any of the limits. It's an Iron Man level tourney. Is it really fair if one person wins because they drafted an obscure herald leveler?