No, Warhawk will be sold on a disc.
IGN: WarHawk Confirmed for Blu-ray
And yes, it includes both ground and air combat. As far as the different airplanes, that I'm not sure about. I do know you can customize your plane (color, emblems, maybe even attachments [don't know]), but I don't know if there's more than two types.
It would make sense either way. On one side, it's two armies fighting, so they only use one specific plane. On the other side, why would they only use one type of airplane? That seems odd to only have one type of aircraft in your airforce.
But whatever happens (two airplanes or ten), I won't mind as long as it's lag free and has kicka$$ gameplay.