The first is a no-brainer, as Clark Gregg is returning as Agent Phil Coulson of S.H.I.E.L.D. Having hammered out the acronym, he gets to come back and try to keep Tony on the straight, narrow, and heroic. I think that's nice. You could just have any old agent, but they're keeping Gregg.
The female addition is what's really interesting. Kate Mara has joined the cast in an unspecified role. I'm going to just throw out a random guess (based largely on her looks) that she's playing Bethany Cabe. I can't believe they'd throw another love interest or action chick into the mix, but Cabe helps to defend Tony against Whiplash and Justin Hammer. She also suits up in some old Iron Man armor alongside Rhodes' War Machine to battle the giant robot Ultimo. The groundwork is there, but it's an awful lot of action and romance for one film. Perhaps Cabe will simply show up as Stark Industries' Head of Security, ready to do her part later on? Maybe she's just a love interest for Hammer? We'll know soon enough.
But wow, three redheads in one Marvel film? I thought it was Wolverine who had that particular fetish. Go Tony!