I don't find any problem with my little guy. He sits behind the passenger seat, but behind the driver shouldn't be much different.
Our baby seat is huge (I've seen the Alpha Omega one, and ours is about that size). As for leg room, I wish I could say, because my son is only 13 months, so his feet don't really hang over yet.
But, if you don't have to put your seat all the way back, I'd think there would be space. At least a little.
Hope that helps.