what sets are going to be legal in the modern age 2007 PC in Indy?

More than 1.

Modern Age should be Heralds of Galactus, Legion of Super-Heroes, Marvel Team-Up and World's Finest. Upper Deck hasn't said wether or not they're tying Hellboy to a certain set for legality purposes or not, or if it would be legal for Modern Age, so nobody knows about that one yet. If they did tie it to a set, it'd most likely be tied to Legion of Super-Heroes.