On circular irimi nage ukemi, I find sliding the inside foot around as your lead foot to be very efficient, both for staying protected and for quick movement, since the circle it travels has a smaller circumference than that of the outside leg. It does take a bit of practice to get used to though.
And as for the fall, if you do a quick pivot on the inside foot and turn to face the direction of the throw , you end up with the correct foot forward. This also takes some practice to perfect. Try unweighting a bit so you can use the ball of your foot as a pivot point and avoid excess torque on the knee.